In C, "if statements" control the program flow based on a condition; it executes some statement code block when the expression evaluates to true; otherwise, it will get skipped. It is the simplest way to modify the control flow of the program.

The if Statement in C can be used in various forms depending on the situation and complexity.

There are four different types of if statements in C. These are:
  • Simple if Statement
  • if-else Statement
  • Nested if-else Statement
  • else-if Ladder

The basic format of the if Statement is:

Syntax:

if(test_expression)
{
    statement 1;
    statement 2;
    ...
}

'Statement n' can be a statement or a set of statements, and if the test expression is evaluated to true, the statement block will get executed, or it will get skipped.

Figure - Flowchart of if Statement:

c-if

Example of a C Program to Demonstrate if Statement

Example:

#include<stdio.h>

void main()
{
    int a = 15, b = 20;

    if (b > a) {  
        printf("b is greater");
    }
}

Program Output:

c-decision-making-if-example1

Example:

#include<stdio.h>

void main()
{
    int number;
    printf("Type a number:");
    scanf("%d", &number);

    if (number < 0) { // check whether the number is negative number.
        number = -number; // If it is a negative then convert it into positive.
        printf("The absolute value is %d\n", number);
    }
} 

Program Output:

c-decision-making-if