Section 3: Program Implementation

Question 1

Low-level languages

Answer 1

These are languages that are machine dependent. Different brands of computers use different program codes. The program code written for a particular brand of CPU will not run on another brand of CPU as the codes are written with the internal operations and architecture of a particular CPU in mind. Examples of low-level languages are Machine language and Assembly language.

Question 2

High-level languages

Answer 2

These are languages that are machine independent. They are not specifically written for any one brand of computer. The program code written on a particular machine is not limited to execution on that machine only but can also run on other similar machines. Examples of high-level languages are Pascal, BASIC, C, etc.

Question 3

First Generation Languages (1GL)

Answer 3

These are low-level languages. They are called machine language and are written using 1’s and 0’s i.e. binary code. It is the only program code that the CPU understands and can obey or execute directly without the need to translate it.

Question 4

Second Generation (2GL)

Answer 4

These are also low-level languages. They are called Assembly language and are written using mnemonic codes- short codes that suggest their meaning and are therefore easier to remember. These codes represent operations, addresses that relate to main memory and storage registers of the computer.

Question 5

Third Generation Languages (3GL)

Answer 5

These are high-level languages. This generation of languages was designed so that it is even easier for humans to understand. They are procedural languages which use simple instructions, written in English, to tell the computer step by step how to solve a problem. A compiler is used to convert the English–like statements to machine language.

Question 6

Fourth Generation (4GL)

Answer 6

These are also high-level languages. Unlike 3GLs, these are non-procedural languages which let you perform computer operations without having to specify all the steps involved. They have built-in methods that can achieve certain goals. 4GLs must be selected to fit a particular application, whereas 3GLs tend to be more general purpose.

Question 7

Fifth Generation (5GL)

Answer 7

These are high-level languages. This generation is essentially 4GLs with a knowledge base. They are designed to build programs that help the computer solve specific problems based on constraints and conditions. They are applied in expert systems, artificial intelligence research and natural language systems. Examples of 5GLs are Prolog, OPS5 and Mercury.

Question 8

Steps in Implementing a Program

Answer 8

1. Create source code
2. Compile source code
3. Link the modules
4. Run/execute program
5. Maintain program

Question 9

Interpreter

Answer 9

An interpreter translates and executes one instruction at a time as it is encountered.

Question 10

Compiler

Answer 10

A compiler translates the entire program (source code) to machine code, and then the machine code is executed. The translated codes are known as object codes.

Question 11

Loading

Answer 11

Reading a program from the hard disk into main memory (RAM)

Question 12

Dry runs/Manual testing

Answer 12

A manual traversal of the logic of a program. After the development of a program the programmer should examine the code to see how it would run.

A dry run is carried out when the action of an algorithm is examined with a set of input values.

A trace table is a useful tool for a dry run, to check how the program would behave.

Question 13

Debugging

Answer 13

The process of correcting or removing errors from a program before it is put into operation.

Question 14

Program Errors

Answer 14

A program error is a mistake/error in a program and is also known as a bug.

Question 15

Logic errors

Answer 15

Arise when the sequence of the instructions is not correct and there are flawed comparisons and selection statements.

Question 16

Syntax errors

Answer 16

Occurs when the source code has not been written in accordance with the rules of the programming language.

Question 17

Run-time errors

Answer 17

Generated during execution of the program. They result when the processor encounters an instruction that violates the processing rules.

Question 18

Loops

Answer 18

The group of statements/instructions to be repeated is called a loop. There are two (2) types:

1. A finite loop – where the number of times a repetition is to be made is known.
2. An infinite loop – where the instructions are repeated an unspecified number of times.

Question 19

WHILE loop

Answer 19

This construct is used when you do not know beforehand how many times a statement within a block needs to be repeated. In this loop the computer executes the instruction to be repeated for as long as a given condition is TRUE. It checks the conditions first and will loop while the condition is true and ends when it is false.

Question 20

FOR loop

Answer 20

This construct is used when the number of times a set of instructions has to be repeated is known.

Question 21

Repeat .. Until Loop

Answer 21

This construct is similar to the WHILE loop, in that, it can be used when you do not know beforehand how many times a statement within a block needs to be repeated. The difference between the WHILE and the REPEAT..UNTIL is that, the computer executes the instruction(s) to be repeated for as long as a given condition remains FALSE and ends when it becomes TRUE. Because of this, the instruction(s) to be repeated is/are always executed at least once.

Question 22

Arrays

Answer 22

Arrays are used to store values of the same type as one variable. An array is a single variable with multiple locations. Each location stores one element/value.

Question 23

Computer testing

Answer 23

Using the computer to run the program with suitable test data (correct and incorrect) to deal with all possible kinds of conditions. The results generated by the computer are then compared with the expected solutions. If the expected and actual results do not match, then the program has a logic error.