Computer studies analysis of questions and answers

KCSE Paper 1 computer studies topical questions and answers dashboard

1/1/2025

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KCSE Paper 1 computer studies topical questions and answers dashboard

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Linkers and Loaders, Review Questions on topic.

20/11/2021

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Linkers & Loaders

Computer programs are usually developed in Modules or Subroutines (i.e., program segments meant to carry out the specific relevant tasks). During program translation, these modules are translated separately into their object (machine) code equivalents.

The Linker is a utility software that accepts the separately translated program modules as its input, and logically combines them into one logical module, known as the Load Module that has got all the required bits and pieces for the translated program to be obeyed by the computer hardware.

The Loader is a utility program that transfers the load module (i.e. the linker output) into the computer memory, ready for it to be executed by the computer hardware.

Syntax

Each programming language has a special sequence or order of writing characters.

The term Syntax refers to the grammatical rules, which govern how words, symbols, expressions and statements may be formed & combined.

Semantics

These are rules, which govern the meaning of syntax. They dictate what happens (takes place) when a program is run or executed.

Review Questions.

Define the following terms:
1. Computer program.
2. Programming.
3. Programming language.
With reference to programming, distinguish between Source program and Object code.
What is the function(s) of: Assemblers, Interpreters and Compilers in a computer system?
1. What are the main functions of a Compiler?
2. Differentiate between a Compiler and an Interpreter.

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Description of terms: assembler, compiler, interpreter, source program, object program

18/11/2021

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Description of terms
1. assembler
2. compiler
3. interpreter
4. source program
5. object program

LANGUAGE TRANSLATORS

A computer uses & stores information in binary form, and therefore, it cannot understand programs written in either high-level or low-level languages. This means that, any program code written in Assembly language or high-level language must be translated into Machine language, before the computer can recognize & run these programs.
A Translator is special system software used to convert the Source codes (program statements written in any of the computer programming languages) to their Object codes (computer language equivalents).

The Translators reside in the main memory of the computer, and use the program code of the high-level or Assembly language as input data, changes the codes, and gives the output program in machine-readable code.
In addition, translators check for & identify some types of errors (e.g., Syntax/grammatical errors) that may be present in the program being translated. They will produce error messages if there is a mistake in the code.

Each language needs its own translator. Generally, there are 3 types of language translators:

Assembler.
Interpreter.
Compiler.

Note. Interpreters & Compilers translate source programs written in high-level languages to their machine language equivalents.

Assembler

An assembler translates programs written in Assembly language into machine language that the computer can understand and execute.

Functions of an Assembler.

It checks whether the instructions written are valid, and identifies any errors in the program.
The Assembler will display these errors as well as the complete source and object programs. If the program has no errors, the job control will let it run immediately, or save the object program so that it may run it later without translating it again.
It assigns memory locations to the names the programmer uses.E.g., the Assembler keeps a table of these names so that if an instruction refers to it, the Assembler can easily tell the location to which it was assigned.
It generates the machine code equivalent of the Assembly instructions.
Usually, the Assembler generates a machine code only when no errors are detected. Some of the errors include;
- Typing mistakes.
- Using the wrong format for an instruction.
- Specifying a memory location outside the range 0 – 2047.

Note. The Assembler cannot detect Logic errors. The programmer knows of these errors only when the program is run & the results produced are incorrect (not what the programmer expected). The programmer must therefore, go through the program & try to discover why an incorrect result was being produced.

Compiler

A compiler translates the entire/whole source program into object code at once, and then executes it in machine language code. These machine code instructions can then be run on the computer to perform the particular task as specified in the high-level program.

The process of translating a program written in a high-level source language into machine language using a compiler is called Compilation.

For a given machine, each language requires its own Compiler. E.g., for a computer to be able translate a program written in FORTRAN into machine language; the program must pass through the FORTRAN compiler (which must ‘know’ FORTRAN as well as the Machine language of the computer).

The object code file can be made into a fully executable program by carrying out a Linking process, which joins the object code to all the other files that are needed for the execution of the program. After the linking process, an executable file with an .EXE extension is generated. This file is stored on a storage media.

Points to note.

The job of a Compiler is much more difficult than that of an Assembler in that, a single statement in a high-level language is equivalent to many machine instructions.
The format of an Assembly instruction is fairly fixed, while high-level languages give a lot of freedom in the way the programmer writes statements.

Functions of a compiler.

A Compiler performs the following tasks during the compilation process:

It identifies the proper order of processing, so as to execute the process as fast as possible & minimize the storage space required in memory.
It allocates space in memory for the storage locations defined in the program to be executed.
It reads each line of the source program & converts it into machine language.
It checks for Syntax errors in a program (i.e., statements which do not conform to the grammatical rules of the language). If there are no syntax errors, it generates machine code equivalent to the given program.
It combines the program (machine) code generated with the appropriate subroutines from the library.
It produces a listing of the program, indicating errors, if any.

Differences between Compilers and Interpreters

Interpreter

Interpreter

Translates & executes each statement of the source code one at a time.
The source code instruction is translated & immediately obeyed by the computer hardware before the next instruction can be translated.
(Translation & execution go together).
Translates the program each time it is needed for execution; hence, it is slower than compiling.
Interpreted object codes take less memory compared to compiled programs.
4. For an Interpreter, the syntax (grammatical) errors are reported & corrected before the execution can continue.
An Interpreter can relate error messages to the source program, which is always available to the Interpreter. This makes debugging of a program easier when using an Interpreter than a Compiler.

Compiler

Translates all the source code statements at once as a unit into their corresponding object codes, before the computer can execute them.
A Compiler translates the entire source program first to machine code, and then the code is executed by the CPU.
(Translation & execution are separate phases)
Compiled programs (object codes) can be saved on a storage media and run when required; hence executes faster than interpreted programs.
Compiled programs require more memory as their object files are larger.
For a Compiler, the syntax errors are reported & corrected after the source code has been translated to its object code equivalent.
Once the source program has been translated, it is no longer available to the Compiler, so the error messages are usually less meaningful.

An interpreter translates a source program word by word or line by line. This allows the CPU to execute one line at a time.

The Interpreter takes one line of the source program, translates it into a machine instruction, and then it is immediately executed by the CPU. It then takes the next instruction, translates it into a machine instruction, and then the CPU executes it, and so on.

The translated line is not stored in the computer memory. Therefore, every time the program is needed for execution, it has to be translated.

Source Program

Source program (source code)

The term Source program refers to program statements that the programmer enters in the program editor window, and which have not yet been translated into machine-readable form.

Source code is the code understood by the programmer, and is usually written in high-level language or Assembly language.

Object Code

Object code (object program).

The term Object code refers to the program code that is in machine-readable (binary) form.

This is the code/language the computer can understand, and is produced by a Compiler or Assembler after translating the Source program into a form that can be readily loaded into the computer.

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Levels of programming languages

18/11/2021

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Levels of programming languages

Low level language
1. machine
2. assembly
High Level languages
1. third Generation Languages (3GLs)
2. four Generation Languages (4 GLs)
3. Object Oriented Programming (OOPs)
4. Internet (scripting) Programming Languages

LEVELS OF PROGRAMMING LANGUAGES

There are many programming languages. The languages are classified into 2 major categories:

Low-level programming languages.
High-level programming languages.

Each programming language has its own grammatical (syntax) rules, which must be obeyed in order to write valid programs, just as a natural language has its own rules for forming sentences.

LOW-LEVEL LANGUAGES

These are the basic programming languages, which can easily be understood by the computer directly, or which require little effort to be translated into computer understandable form.
They include:

Machine languages.
Assembly languages.

Features of low-level languages

They are machine hardware-oriented.
They are not portable, i.e., a program written for one computer cannot be installed and used on another computer of a different family.
They use Mnemonic codes.
They frequently use symbolic addresses.

Machine languages (1st Generation languages)

Machine language is written using machine codes (binary digits) that consist of 0’s & 1’s.

The computer can readily understand Machine code (language) instructions without any translation.

A programmer is required to write his program in strings of 0’s & 1’s, calculate & allocate the core memory locations for his data and/or instructions.

Different CPU’s have different machine codes, e.g., codes written for the Intel Pentium processors may differ from those written for Motorola or Cyrix processors. Therefore, before interpreting the meaning of a particular code, a programmer must know for which CPU the program was written.

A machine code instruction is made up of 2 main parts;

An Address (operand):
It specifies the location (address) of the computer memory where the data to be worked upon can be found.
A Function (operation) code:
It states to the Control Unit of the CPU what operation should be performed on the data/item held in the address, e.g., Addition, Subtraction, Division, Multiplication, etc.

Note. The computer can only execute instructions which are written in machine language. This is because; it is the only language which the computer can understand. Therefore, any program written in any other programming language must first be translated into machine language (binary digits) before the computer can understand.

Assembly language (2nd Generation Languages).

Assembly languages were developed in order to speed up programming (i.e., to overcome the difficulties of understanding and using machine languages).

The vocabulary of Assembly languages is close to that of machine language, and their instructions are symbolic representations of the machine language instructions.

Assembly language programs are easier to understand, use & modify compared to Machine language programs.
Assembly language programs have less error chances.

To write program statements in Assembly language, the programmer uses a set of symbolic operation codes called Mnemonic codes.

The code could be a 2 or 3 shortened letter word that will cause the computer to perform specific operation. E.g., MOV – move, ADD - addition, SUB – subtraction, RD - read.

Example;
RD PAT, 15 (read the value 15 stored in the processor register named PAT)
SUB PAT, 10 (subtract 10 from the value in register PAT)

A program written in an Assembly language cannot be executed/obeyed by the computer hardware directly. To enable the CPU understand Assembly language instructions, an Assembler (which is stored in a ROM) is used to convert them into Machine language.

The Assembler accepts the source codes written in an Assembly language as its input, and translates them into their corresponding computer language (machine code/ object code) equivalent.

Comments are incorporated into the program statements to make them easier to be understood by the human programmers.

Assembly languages are machine-dependent. Therefore, a program written in the Assembly language for a particular computer cannot run on another make of computer.

Advantages of Low-level languages

The CPU can easily understand machine language without translation.
The program instructions can be executed by the hardware (processor) much faster. This is because; complex instructions are already broken down into smaller simpler ones.
Low-level languages have a closer control over the hardware, are highly efficient & allow direct control of each operation.
They are therefore suitable for writing Operating system software & Game programs, which require fast & efficient use of the CPU time.
They require less memory space.
Low-level languages are stable, i.e., they do not crash once written.

Disadvantages of Low-level languages

Very few computer programs are actually written in machine or Assembly language because of the following reasons;

Low-level languages are difficult to learn, understand, and write programs in them.
Low-level language programs are difficult to debug (remove errors from).
Low-level languages have a collection of very detailed & complex instructions that control the internal circuiting of the computer. Therefore, it requires one to understand how the computer codes internally.
Relating the program & the problem structures is difficult, and therefore cumbersome to work with.
The programs are very long; hence, writing a program in a low-level language is usually tedious & time consuming.
The programs are difficult to develop, maintain, and are also prone to errors (i.e., it requires highly trained experts to develop and maintain the programs).
Low level languages are machine-dependent (specific), hence non-portable.
This implies that, they are designed for a specific machine & specific processor, and therefore, cannot be transferred between machines with different hardware or software specifications.
It is not easy to revise the program, because this will mean re-writing the program again.

HIGH-LEVEL PROGRAMMING LANGUAGES

High-level languages were developed to solve (overcome) the problems encountered in low-level programming languages.

The grammar of High-level languages is very close to the vocabulary of the natural languages used by human beings. Hence; they can be read and understood easily even by people who are not experts in programming.

Most high-level languages are general-purpose & problem-oriented. They allow the programmer to concentrate on the functional details of a program rather than the details of the hardware on which the program will run.

High-level language programs are machine-independent, (i.e., they do not depend on a particular machine, and are able to run in any family of computers provided the relevant translator software is installed).

Programs written in a high-level language cannot be obeyed by the computer hardware directly. Therefore, the source codes must be translated into their corresponding machine language equivalent. The translation process is carried out by a high-level language software translator such as a Compiler or an Interpreter.

Features of high-level programming languages.

They contain statements that have an extensive vocabulary of words, symbols, sentences & mathematical expressions, which are very similar to the normal English language.
Example;
Read (TaxablePay);
IF TaxablePay<1000 THEN
Tax: =0;
ELSE
Tax: =TaxRate * TaxablePay;
Write (Tax: 6:2);
Allow modularization (sub-routines).
They are ‘user-friendly’ and problem-oriented rather than machine-based. This implies that, during a programming session, the programmer concentrates on problem-solving rather than how a machine operates.
They require one to be obey a set of rules when writing the program.
Programs written in high-level languages are shorter than their low-level language equivalents, since one statement translates into several machine code instructions.
The programs are portable between different computers.

Purpose of High-level languages.

To improve the productivity of a programmer. This is because; the source programs of high-level languages are shorter than the source programs of low-level languages, since one statement translates into several machine code instructions.
To ease the training of new programmers, since there is no need to learn the detailed layout of a procession/sequence.
To speed up testing & error correction.
To make programs easy to understand & follow.

Advantages of High-level languages.

They are easily portable, i.e., they can be transferred between computers of different families and run with little or no modification.
High-level language programs are short, and take shorter time to be translated.
They are easy to lean, understand and use.
They are easy to debug (correct/remove errors), & maintain.
High level language programs are easy to modify, and also to incorporate additional features thus enhancing its functional capabilities.
They are ‘user-friendly’ & problem-oriented; hence, can be used to solve problems arising from the real world.
They enable programmers to adapt easily to new hardware. This is because; they don’t have to worry about the hardware design of the computer.
High-level language programs are self-documenting, i.e., the program statements displays the transparency of purpose making the verification of the program easy.
High level languages are more flexible; hence, they enhance the creativity of the programmer and increase his/her productivity in the workplace.

Disadvantages of using High-level languages

High-level languages are not machine-oriented; hence, they do not use of the CPU and hardware facilities efficiently.
The languages are machine-independent, and cannot be used in programming the hardware directly.
Each high-level language statement converts into several machine code instructions. This means that, they use more storage space, and it also takes more time to run the program.
Their program statements are too general; hence, they execute slowly than their machine code program equivalents.
They have to be interpreted or compiled to machine-readable form before the computer can execute them.
The languages cannot be used on very small computers.
The source program written in a high-level language needs a Compiler, which is loaded into the main memory of the computer, and thus occupies much of memory space. This greatly reduces the memory available for a source program.

TYPES OF HIGH-LEVEL LANGUAGES

High-level languages are classified into five different groups:

Third generation languages (Structured / Procedural languages).
Fourth generation languages (4GLs).
Fifth generation languages (5GLs)
Object-oriented programming languages (OOPs).
Web scripting languages.

The various types of high-level languages differ in:

The data structures they handle.
The control structures they support.
The assignment instructions they use.
Application areas, e.g., educational, business, scientific, etc.

STRUCTURED LANGUAGES

A structured (procedural) language allows a large program to be broken into smaller sub-programs called modules, each performing a particular (single) task. This technique of program design is referred to as structured programming.

Structured programming also makes use of a few simple control structures in problem solving. The 3 basic control structures are:

Sequence
Selection.
Iteration (looping).

Advantages of structured programming.

It is flexible.
Structured programs are easier to read.
Programs are easy to modify because; a programmer can change the details of a section without affecting the rest of the program.
It is easier to document specific tasks.
Use of modules that contain standard procedures throughout the program saves development time.
Modules can be named in such a way that, they are consistent and easy to find in documentation.
Debugging is easier because; each module can be designed, coded & tested independently.

Examples of Third generation programming languages include:

BASIC (Beginners All-purpose Symbolic Instructional Code).
BASIC is a simple general-purpose high-level language used in most computer processing tasks such as developing business and educational applications.
It is easy to learn & use; hence, suitable for students who wish to easily learn programming.
Translation in most versions of BASIC is carried out by an Interpreter.
Disadvantages of BASIC.
-BASIC is available in so many versions with different dialects/languages & therefore, it has no standard.
-Some dialects are limited to data & control structures they support.
-Some versions of BASIC offer limited facilities in terms of structured programming & meaningful variable names.
PASCAL
PASCAL is a general-purpose, high-level programming language, which was named after a French mathematician called Blaise Pascal.
It was developed as an academic tool to help in the teaching and learning of structured programming.
PASCAL supports structured programming, i.e., it uses procedures & functions, which allow a ‘top-down’ approach to solving problems.
-It is not easy to learn because; it has strict rules in its grammar on typing of variables (data names) & declarations.
-It is poor (has limited ability) on handling of data files.
COBOL (Common Business Oriented Language)
COBOL is designed for developing programs that solve business problems, e.g., can be used to develop commercial data processing applications such as computer-based inventory control systems. COBOL is mostly used where large amounts of data are to be handled, because it supports powerful data & control structures. COBOL programs are semi-compiled, and the intermediate code is interpreted. A program written in COBOL language consists of 4 divisions: -
(i). Identification division: Where the programmer & the program details are specified, e.g., program ID, programmer name, etc.
(ii). Environment division: Where the equipment to be used by the source & the object programs are defined, e.g., the computer hardware.
(iii). Data division: Where the various files to be used by the program are described, e.g., a description of the input files.
(iv). Procedure division: Where all the procedures required to manipulate/interrelate the data into information are defined.
Advantages of COBOL.
-It is easy to read.
-It is portable, i.e., can be used on different types of computers. This is because; it has an American National Institute standard.
American National Standards Institute (ANSI): – An international organization that devised/ invented the group of standardized symbols used in flowcharting.
-It is widely used, and has a pool of skilled programmers.
Disadvantage of COBOL.
The structure of a COBOL program is too long even for simple programs.
E.g., consider the following assignment statement:
DIVIDE A into B giving C.
This statement when used in BASIC language can much short ‘C=A/B’. However, notice that the COBOL statement above is more self defining.
FORTRAN (FORmula TRANslator)
It was developed for mathematicians, scientists and engineers. It provides an easier way of writing scientific & engineering applications.
FORTRAN statements are mostly in form of mathematical expressions; hence, it is useful in writing of programs that can process numeric data.
FORTRAN programs are compiled.
Advantages of FORTRAN.
-It is portable, i.e. it can be used on different types of computers.
Disadvantage of FORTRAN.
It is not suited for business applications.
Ada
This language was named after the first lady programmer Ada Lovelace.
It is suitable for developing military, industrial and real-time systems.
C
C is mainly used for developing system software such as the operating system as well as developing the application packages.
It has powerful commands that permit the rapid development of programs, and allows direct control over the hardware.
Disadvantage of C
It is difficult to read & learn because of its strict dialect rules.
LOGO
LOGO was designed for educational use in which children can explore & develop concepts through programming the movement of a pen.
COROL
COROL is used in Real-time processing.
COROL programs are compiled.
RPG (Report Program Generator)
RPG is used in report generating applications, (i.e. it is designed to facilitate the output of reports of business data).
A Report generator is a software tool that extracts stored data to create customized reports that are not normally/usually produced by existing applications.
SNOBOL (String Oriented Symbolic Language).
It is a high-level language designed to manipulate strings of characters. It is therefore used for non-numeric applications.

FOURTH GENERATION LANGUAGES (4GL’S).

4GLs make programming even easier than the 3GLs because; they present the programmer with more programming tools, such as command buttons, forms, textboxes etc. The programmer simply selects graphical objects called controls on the screen, and then uses them to create designs on a form by dragging a mouse pointer.

The languages also use application generators (which in the background) to generate the necessary program codes; hence, the programmer is freed from the tedious work of writing the code.

4GLs are used to enquire & access the data stored in database systems; hence, they are described as the Query languages.

Purpose of fourth generation languages.

The 4GL’s were designed to meet the following objectives: -

To speed up the application-building process, thereby increasing the productivity of a programmer.
To enable quick & easy amendments and alteration of programs.
To reduce development & maintenance costs.
To make languages user-friendly. This is because, the 4GL’s are designed to be user-oriented, unlike the 3rd generation languages which are problem & programmer oriented.
To allow non-professional end-users to develop their own solutions.
To generate bug-free codes from high-level expressions of requirements.

Examples of 4GLs are:

Visual Basic
Delphi Pascal
Visual COBOL (Object COBOL)
Access Basic

Advantages of fourth generation languages.

They are user-based, and therefore, easy to learn & understand.
The grammar of 4GL’s is very close to the natural English language. It uses menus & prompts to guide a non-specialist to retrieve data with ease.
Very little training is required in order to develop & use 4GL programs.
They provide features for formatting of input, processing, & instant reporting.

FIFTH GENERATION LANGUAGES (5GL’S).

The 5GL’s are designed to make a computer solve a problem by portraying human-like intelligence.

The languages are able to make a computer solve a problem for the programmer; hence, he/she does not spend a lot of time in coming up with the solution. The programmer only thinks about what problem needs to be solved and what conditions need to be met without worrying about how to implement an algorithm to solve the problem.

5GLs are mostly used in artificial intelligence.

Examples of 5GLs are:

PROLOG
LISP
Mercury
OCCAM.

LISP (LISt Processing)
In LISP, both programs & data are arranged (structured) as lists.
It is used in artificial intelligence. However, it is not suitable for commercial data processing applications.
PROLOG (PROgramming in LOGic)
PROLOG was developed from LISP by the Japanese.
It is designed for use with Expert systems & Artificial Intelligence. It is mostly used for solving problems, which involve objects and relationships between objects.
Like LISP, it is not suitable for commercial data processing applications.

OBJECT-ORIENTED PROGRAMMING LANGUAGES (OOPs)

Object-Oriented Programming is a new approach to software development in which data & procedures that operate on data are combined into one object.
OOPs use objects. An Object is a representation of a software entity such as a user-defined window or variable. Each object has specific data values that are unique to it (called state) and a set of the things it can accomplish called (functions or behaviour).
Several objects can be linked together to form a complete program. Programs send messages to an object to perform a procedure that is already embedded in it. This process of having data and functions that operate on the data within an object is called encapsulation.
The data structure & behaviour of an object is specified/described by a template (called a class). Classes are hierarchical, and it is possible to pass the data & behaviour of an object in one class down the hierarchy.
Object-Oriented programming enables rapid program development. Every object has properties such as colour, size, data source, etc, which can be set easily without much effort. In addition, every object has events associated with it that can be used to trigger certain actions, e.g. remove the window from the screen on clicking the ‘Close’ button.
OOP has contributed greatly to the development of graphical user interface operating systems and application programs.

Examples of Object-oriented programming languages are: -

Simula
C++
SmallTalk
Java

Java is sometimes associated with development of websites, but it can be used to create whole application programs that do not need a web browser to run.

JAVA

Java is an OOP language that resembles Object C (a simplified form of C++).
The code of Java displays graphics, accesses the network, and interfaces with users via a set of capabilities known as classes. Classes define similar states & common methods for the behavior of an object.
JAVA programs are not compiled into machine code; instead, they are converted into a collection of bytes that represent the code for an abstract Java Virtual machine (VM). A Java interpreter running on a physical machine is then used to translate those bytes into local actions, such as printing a string or drawing a button.

WEB SCRIPTING LANGUAGES.

Web scripting languages are mostly used to create or add functionalities on web pages.
Web pages are used for creating Web sites on the Internet where all sorts of advertising can be done.
Web pages are hypertext (plain-text) documents written using a language called HyperText Markup Language (HTML). HTML documents have a file extension of .Html or .Htm.
Note. HTML doesn’t have the declaration part and control structures, and has many limitations. Therefore, to develop functional websites, it must be used together with other web scripting languages like JavaScript, VBScript and Hypertext Preprocessor.

Comparison of Programming languages.

Machine language

Instruction set is made up of binary digits (0’s & 1’s).
Instruction is made of 2 parts: operation code & operand.
No translation is needed. (This is the computer language; hence, the computer understands it directly).
Executed by the hardware directly & is faster.
Difficult to learn, develop & maintain.
Programs are lengthy & tedious.
It is time-consuming to develop machine code programs.
Used in applications where efficient use of the CPU time is necessary, e.g., developing Operating systems & other Control programs that coordinate the working of peripherals.

Assembly language

Instruction set is made up of Mnemonics & labels.
Instruction is made up of 2 parts: operation code & operand, but comments can be added.
Uses an Assembler to convert the assembly language source codes to their object code equivalents
Executed faster than High-level, but slower than the machine code programs.
It’s easier to learn, develop & maintain as compared to machine code programs.
Like machine code language, the programs are lengthy & tedious.
They take a shorter time to develop as compared to machine code programs, but take longer than High-level language programs.
Like machine language, Assembly language programs are used in applications where efficient use of the CPU time is necessary.

High-level languages

Instruction set is similar to English language statements & mathematical operators.
The instruction varies depending on the particular language.
Uses compiler or interpreter - Compiler translates all the source code at once into object code; Interpreter translates line by line.
Translation & execution is very slow.
Easy to learn, develop, maintain and use.
Programs are shorter & simpler than Machine & assembly lang. programs.
Developing High-level language programs takes very short time.
Most High-level languages are general-purpose, & can be used to do almost all computer-processing tasks.

Factors to consider when choosing a Programming language.

The following factors should be considered when choosing a Programming language to use in solving a problem:

The availability of the relevant translator
Whether the programmer is familiar with the language
Ease of learning and use
Purpose of the program,
i.e., application areas such as education, business, scientific, etc.
Execution time
Applications that require quick response are best programmed in machine code or assembly language. High-level languages are not suitable for such application because, they take long to be translated & executed.
Development time
Development time is the time a programmer takes to write and run a program. - High-level languages are easy to read, understand and develop; hence, they require less development time. Machine code & Assembly languages are relatively difficult to read, understand and develop; hence, they are time-consuming.
Popularity
The language selected should be suitable and/or successful in the market with respect to the problems to be solved.
Documentation
It should have accompanying documentation (descriptions) on how to use the language or maintain the programs written in the language.
Maintenance
Programs are developed to solve specific problems, and the problems keep on changing; hence, the programs are also changed to perform the new functions. Program maintenance is the activity of incorporating more routines onto the program, modifying the existing routines or removing the obsolete routines to make the program adapt to a functionally enhanced environment. The maintenance is made easier if the language used is easy to read and understand.
Availability of skilled programmers
The language selected should have a pool of readily available programmers to ease the programming activity, and reduce development time.

Review Questions

(a). What is a Programming language?
(b). Explain the two levels of programming languages.
(a). What is meant by ‘Machine language’?
(b). Explain why machine language programming is so error-prone.
(c). Show the difference between Machine language and Assembly language.
(d). Give two advantages & three disadvantages of Machine language programming.
(a). What are High-level languages?
(b). Give the features/characteristics of high-level programming languages.
(c). Describe briefly how a program written in high-level programming language becomes a machine code program ready for operational use.
(d). Explain the advantages and disadvantages of using a High-level programming language for writing a program.
(e). List four examples of high-level programming languages. Indicate the application of each language in computing.
(a). What is meant by program portability?
(b). Why are low-level languages not considered to be portable?
List 8 factors that need to be considered when selecting a programming language.

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Definition of Programming

18/11/2021

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Definition of Programming

Computer Program:

A computer program is a set of coded instructions given to the computer, and represents a logical solution to a problem. It directs a computer in performing various operations/tasks on the data supplied to it.

Computer programs may be written by the hardware manufacturers, Software houses, or a programmer to solve user problems on the computer.

Programming:

Programming is the process of designing a set of instructions (computer programs) which can be used to perform a particular task or solve a specific problem.

It involves use of special characters, signs and symbols found in a particular programming language to create computer instructions.

The programming process is quite extensive. It includes analyzing of an application, designing of a solution, coding for the processor, testing to produce an operating program, and development of other procedures to make the system function.

The program created must specify in detail the logical steps to be taken & the method of processing the data input into the computer in order to carry out the specified task.

A computer program performs the following:

Accepts data from outside the computer as its input.
Carries out a set of processes on the data within the computer memory.
Presents the results of this processing as its output, and
Stores the data for future use.

Programming Languages:

A programming language is a set of symbols (a language) which a computer programmer uses to solve a given problem using a computer.

The computer must be able to translate these instructions into machine-readable form when arranged in a particular sequence or order.

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List four areas that would be considered in the requirement specification.

18/11/2021

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(a) List and describe four strategies for converting from an old system to a new system. (4mks)

Direct approach
user simply stops using old system and starts using the new one
Parallel approach
old and new system are operated side by side until the new system has shown it is reliable
Phased approach
parts of a new system are phased in separately either at different times or all at one in groups
Pilot approach
entire system is tried out but only by some users

(b) (i) Distinguish between private data and confidential data (2mks)

Private data
belongs to an individual and must be accessed through direct permission from the owner
Confidential data
held by government or organization about people but can be seen by authorized people only.

(ii) What can be done to stop illegal access to a computer laboratory by unauthorized people (3mks)

fit strong metallic grills and locks to doors
don’t welcome strangers into the lab
install alarms
employ guards
burglar proof

(c) (i) List four areas that would be considered in the requirement specification. (4mks)

output specification
in put specification
file /data/tables
hard ware/soft ware

(ii) Name any two areas covered in feasibility report during system analysis and design. (2mks)

Lost benefit analyst
Schedule
Users
Environment
Technology

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A computer diskette in drive A has folders for MEMOS for an administrator. Each of these folders is labelled according to the relevant months.

17/11/2021

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A computer diskette in drive A has folders for MEMOS for an administrator. Each of these folders is labelled according to the relevant months. The secretary created the folders for each month’s memo for each of access. Study the table below

A computer diskette in drive A has folders for MEMOS for an administrator. Each of these folders is labelled according to the relevant months. The secretary created the folders for each month’s memo for each of access. Study the table below

(a) Assuming that the secondary was working from the diskette, draw the corresponding tree structure (6mks)

(b) (i) The secretary wanted to create a folder to store a memo in Fraud folder. State the path for that folder. (2mks)

A:/MEMO2/Fraud

(ii) Suggest how the secretary can ensure that the work in that diskette is not spoilt. (1mk)

do not drop the diskette down
don’t put heavy objects on top
don’t put near magnets
don’t remove from drive when still being read / written

(iii) The content of the file is not viewed by any other person apart from her. (1mk)

use of password

(c) (i) List any two devices under the control of the operating system. (2mks)

I/O
CPU
memory
secondary storage
communication & ports

(ii) Explain how each one of these devices are controlled by the OS - Operating System

Input/output devices and ports
In most cases, the operating system controls all data input and information output tasks. Because most input/output devices are slower than the processor, the operating system has to control the flow of data from the time of input to the time the user receives it as information. It ensures that the right data reaches the processor at the right time. The operating system also defines the various input/output ports found on the computer e.g. printer port.

The processor
The processor is a scarce resource. It executes tasks called processes. At any one time several tasks may require processing hence creating competition. The operating system arranges the tasks according to priority and has the ability to stop a particular task to allow the processor to service another one.

Main memory(RAM)
At any one given time so many tasks may require the memory so that they can be accessed and processed by the computer.However,because memory is also a scarce resource,the operating system determines which task will remain in memory awaiting for execution and which one will be sent back to secondary storage to wait.

Because the operating system is large and very important, it is usually installed on the hard disk but must be loaded to RAM during the booting process. Not all the operating system can fit in RAM so a small special part that contains the most necessary commands and procedures called the kernel is the one that is loaded.

Secondary storage devices
The operating system manages the storage and retrieval of data on secondary storage devices. It also utilizes the free space on hard disks to enhance the performance of the computer by temporarily holding tasks on it that were in RAM ready for processing but have to wait for sometime.

Communication devices and ports
Communication in this case refers to how the various devices and programs in and out of the computer system send and receive messages from one another and from the processor. The operating system controls the overall communication process between various tasks and computers. External communication can be achieved by connecting an external device to a communication port using a communication medium like cables or even wireless communication.

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The information below is maintained by the sales lady at the school canteen. Study it and answer the questions that follow.

17/11/2021

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The information below is maintained by the sales lady at the school canteen. Study it and answer the questions that follow.

(a) Describe the basic data types used in this spreadsheet (4mks)

Labels
describing items names
Values
describing units on column B and C

(b) Provide a single formula that would be used to
(i) Count the number of items whose units are equal; to 15 (2mks)

=COUNTIF(B2:B5,15) or =COUNTIF(B2:B5,=15)

(ii) Sum the values of items whole units are equal to 12 (2mks)

=SUMIF(B2:B5,"=12") or =SUMIF(B2:B5,"12")

(c) (i) List and describe four areas of application of spreadsheets (4mks)

Accounting
What IF analysis (forecasting)
Budgeting
Calendars
Expense reports
Forms
Time sheets
Invoices
Purchase Orders
Receipts
Schedules

(ii) Explain data range legend and axis as used in spreadsheet charts (3mks)

Axis

A reference line from \which distances or angles are measured in a coordinate system, such as the X-axis and y-axis in the Cartesian coordinate system

Legend

Brief description accompanying an illustration (chart) also known as a caption

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List three advantages and three disadvantages of fibre optic cable and Name two types of coaxial cables

17/11/2021

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(a) List three advantages and three disadvantages of fibre optic cable (6mks)
Advantages

immune to electro magnetic interference and ear dropping
fast and supports high band width
large distance can be covered because it has low attenuation
can be used in hazardous environment
smaller and lighter than copper

Disadvantages

connecting devices are expensive
installation is difficult
complex to configure
expensive/ difficult to repair

(b) Describe the following signals and state where each is applied in network communication. (4mks)
Analog

made up of continuous varied wave form.
it is transmitted over telephone line.
a codec converts an analog signal to digital for transmission via a digital medium

Digital

made up of non continuous discrete wave form computers
a modem converts a digital signal to analog for transmission over the analog media

(c) Name two types of coaxial cables (2mks)

thin net
thick net

(d) (i) Distinguish between microwave and satellite transmissions. (2mks)

Microwave transmission consists of point to point transmissions meaning a signal is divided through a focused beam from transmitter to receiver while satellite is usually launched into speck

(ii) Give an example of internet protocol (1mk)

ICPIP [Internet Control Message Protocol]
TCP [Transmission Control Protocol]
IP [Internet Protocol]

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Describe three methods you would use in error detection during program testing

16/11/2021

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(a)When invoicing customers, the invoice clerk has to work out the discounts allowable on each order. Any order over 20,000/= attracts a “bulk” discount of 7%. A customer within the trade is allowed 10%. There is also a special discount of 2% allowed for any customer who has been ordering regularly for over 2 years. Using a flowchart show clerical procedure for working out discount entitlement.

When invoicing customers, the invoice clerk has to work out the discounts allowable on each order. Any order over 20,000/= attracts a “bulk” discount of 7%. A customer within the trade is allowed 10%. There is also a special discount of 2% allowed for any customer who has been ordering regularly for over 2 years. Using a flowchart show clerical procedure for working out discount entitlement.

(b) Name the control structures you have used in the flow chart (2mks)

selection
sequence

Describe three methods you would use in error detection during program testing

error detection methods

desk checking (dry-run)
going through the program while still on paper
using debugging utilities
enter the program editor where syntax errors are detected during translation
using test date
carries out trial runs
various data variations and extreme including good and bad data are entered to see how the program would handle them

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Explain the terms computer fraud and alteration.

16/11/2021

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Explain the following terms. (2mks)

(a) Computer fraud

use of computer to conceal information or cheat other people with the intention of gaining money or information

Explain the terms computer fraud and alteration

(b) Alteration

the legal charging of data or information with the intention of misinforming authorized users or gaining

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List four stages in data collection. What is meant by reference and report file

16/11/2021

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(a) List four stages in data collection. (2mks)

creation
transmission
preparation
media conversion
input validation
sorting

(b) What is meant by the following (2mks)
(i) Reference file

used for reference or lookup purposes that is required during processing

(ii) Report file

used to store permanent records extracted from the master file or generated after processing operation

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List four types of publications that can be designed using DTP software.

16/11/2021

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List four types of publications that can be designed using DTP software. (2mks)

Cards,
certificate,
newspapers,
magazines,
pamphlets,
newsletters,
books,
calendars,
Adverts,
Banners
Price lists and Hotel Menus

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List three ways by which you can provide a common link or relationship between the tables in a database software

15/11/2021

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(a) List three ways by which you can provide a common link or relationship between the tables in a database software. (3mks)

one -to -one
one – to – many
many – to – many

(b) What is referential integrity (1mk)

relationship based on primary and foreign keys
a feature that governs the nature of records in a one – to – many relationship between tables in database

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Write an algorithm to computer the area of a circle.

15/11/2021

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Write an algorithm to computer the area of a circle. (2mks)

Pseudocode

Start
input
pie = 3.14
area = pie*r*r
print area
end

Start
input
area = 3.14 *r*r
print r, area
stop

Flowchart

Write an algorithm to computer the area of a circle.

flowchart

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<<Previous

COMPUTER STUDIES TOPICAL QUESTIONS AND ANSWERS FOR REVISION

A

Level/Form

Section

Year of Examinations

B

C

D

E

F

H

I

L

M

N

O

P

R

S

T

U

W

​​Linkers & Loaders

​Syntax

​Semantics

​Review Questions.

​LANGUAGE TRANSLATORS

Assembler

​Functions of an Assembler.

Compiler

​Functions of a compiler.

​Differences between Compilers and Interpreters

Interpreter

Source Program

Object Code

​LEVELS OF PROGRAMMING LANGUAGES

​LOW-LEVEL LANGUAGES

​Features of low-level languages

​Machine languages (1st Generation languages)

​Assembly language (2nd Generation Languages).

​Advantages of Low-level languages

​Disadvantages of Low-level languages

​HIGH-LEVEL PROGRAMMING LANGUAGES

​Features of high-level programming languages.

​Purpose of High-level languages.

​Advantages of High-level languages.

​Disadvantages of using High-level languages

​TYPES OF HIGH-LEVEL LANGUAGES

​STRUCTURED LANGUAGES

Linkers & Loaders

Syntax

Semantics

Review Questions.

LANGUAGE TRANSLATORS

Functions of an Assembler.

Functions of a compiler.

Differences between Compilers and Interpreters

LEVELS OF PROGRAMMING LANGUAGES

LOW-LEVEL LANGUAGES

Features of low-level languages

Machine languages (1st Generation languages)

Assembly language (2nd Generation Languages).

Advantages of Low-level languages

Disadvantages of Low-level languages

HIGH-LEVEL PROGRAMMING LANGUAGES

Features of high-level programming languages.

Purpose of High-level languages.

Advantages of High-level languages.

Disadvantages of using High-level languages

TYPES OF HIGH-LEVEL LANGUAGES

STRUCTURED LANGUAGES