Unit 1 Introduction to Computer Programs

Unit 1: Introduction to Computer Programs Computer program and Programming Languages Computer program is a set of instructions that, when executed, causes the computer to behave in a predetermined manner. Without programs, computers are useless and can do nothing. Computers cannot understand human natural languages like English or Nepali. To instruct a computer to perform a certain job, we need languages which can be understood by the computer. The languages which are used to instruct the computer to do certain jobs are called ​computer programming languages. Types or Levels of Programming Languages There are two ​types of programming languages​, which can be categorized into the following ways: 1. Low level language ● Machine language (1GL) ● Assembly language (2GL) 2. ● ● ● High level language Procedural-Oriented language (3GL) Problem-Oriented language (4GL) Natural language (5GL) Low Level Language: This language is the most understandable language used by computers to perform its operations. It can be further categorized into: a) Machine Language (1GL) Machine language consists of strings of binary numbers (i.e. 0s and 1s) and it is the only one language, the computer directly understands. Machine language has a merit of very fast execution speed and efficient use of primary memory. Example: To add two numbers 3 and 6 in machine language program may be like: 11 3 10111001 Machine code for addition(say) 110 6 Merits: ● It is directly understood by the computer so has faster execution time since the programs written in this language need not be translated. ● It doesn’t need a larger memory. Demerits: ● It is very difficult to program using 1GL since all the instructions are to be represented by 0s and 1s. ● Use of this language makes programming time consuming. ● It is difficult to find errors and to debug. ● It can be used by experts only. b) Assembly Language Assembly language is also known as low-level language because to design a program programmer requires detailed knowledge of hardware specification. This language uses mnemonics code (symbolic operation code like ‘ADD’ for addition) in place of 0s and 1s. The program is converted into machine code by the assembler. Example: To add two numbers 3 and 6 in machine language program may be like: 11 ADD 110 Some of the commonly used mnemonics are: CODE ADD SUB INR DCR CMP Meaning Addition Subtraction Increase Decrease Compare Merits: ● It makes programming easier than 1GL since it uses mnemonics code for programming. Eg: ADD for addition, SUB for subtraction, DIV for division, etc. ● It makes the programming process faster. ● Error can be identified much more easily compared to 1GL. ● It is easier to debug than machine language. Demerits: ● Programs written in this language are not directly understandable by computer so translators should be used. ● It is a hardware dependent language so programmers are forced to think in terms of the computer's architecture rather than to the problem being solved. High level language Instructions of this language closely resemble human language or English like words. It uses mathematical notations to perform the task. The high level language is easier to learn. It requires less time to write and is easier to maintain the errors. The high level language is converted into machine language by one of the two different languages translator programs; ​interpreter or compiler. High level language can be further categorized as: a) Procedural-Oriented language (3GL) Procedural Programming is a methodology for modeling the problem being solved, by determining the steps and the order of those steps that must be followed in order to reach a desired outcome or specific program state. These languages are designed to express the logic and the procedure of a problem to be solved.