Introduction

We have seen  that a C program is a set of statement which are normally executed sequentially in the order in which they appear. This happens when no option or no repetitions of certain calculation are necessary . However , in practice  , we have a number of situation where we many have to change the order of execution of statement based on certain conditions, or repeat group of statements until certain  specified condition are met.

C language possesses such decision - making capabilities by supporting the following statement

1. if statement
2. switch statement
3. conditional operator statement
4. goto statement

These statements are popularly known as decision - making statements. Since these statements 'control' the flow of execution , they are also known as control statements.

Decision Making With If Statement

The if statement is a powerful decision - making system statement and it used to control flow of execution of statement . It is basically a two - way decision statement and in conjunction with an expression .It allows the computer to evaluate the expression first and then , depending on whether the value of the expression (relation or condition) is 'true' ( or non-zero) or 'false' (zero), it transfers the control to a particular statement.

Some examples of decision making, using if statements are:

1. if (bank balance is zero)
borrow money

2. if (room is dark )
put on lights

The if statement may be implemented in a different form s depending on the complexity of condition to be tested. The different forms are:

1. Simple if statement
2. if ......else statement
3. Nested if ......else statement
4. else if statement.

Simple If Statement

The general form simple if statement is
 
The statement block may be single statement or a group statements if the test expression is true, the statement block will be executed : otherwise the statement block will be execution will jump to  the statement - x . Consider the following  segment of a program that is written for processing of marks obtained in an entrance examination.




The program tests the type of category of the student . If the student belongs to the SPORTS category , then additional bonus _ marks are added to his marks before they are printed. For other bonus_ marks are not added.