C programming if, if .. else and nested if .. else statements

In this tutorial, you will learn to control flow control of a program using c programming if statement.

Normally, statements in a program are executed one after the other in the order in which they are written. This is called sequential execution.

But sometimes, along with the program, the order of execution needs to be changed or the programmer must know how to change the flow of the program.

For this C provides control statement if and if..else to control the flow of program.

C programming if statement

It’s a one-way branching in which the statements will only execute if the given expression is true.

if ( expression)
 {
   statements;
 }

Here, statements will be executed only if the expression is true.

Flowchart of if statement

C programming if else statement

if..else statement is used if we want to execute some code if the condition is true and another code if the condition is false.

syntax of if..else statement

Here, if an expression is true then statement1 will be executed , otherwise,  statement2 will be executed.

if (expression)
 {
   statement1;
 }
else
 {
   statement2;
 }

Here, if the expression is true then statement1 will be executed otherwise, statement2 will be executed.

Example: if grades are less than 40 you will get failed result, otherwise you will get pass result

#include <stdio.h>
int main ()
 {
    int grades;
    printf("enter your grades :");
    scanf("%d",&grades);
    if ( grades >= 40 )
      printf("Congratulations you are passed");
    else
      printf("Sorry you are failed");
    return 0;
 }

 Output

enter your grades : 50
Congratulations you are passed

if..else if…else statement

if...else if...else statement is used to select a particular block of code when several block of codes are there.

structure of if..else if.. else statement

	if(expression1)
 	 {
 	   statement1;
 	 }
 	else if (expression2)
 	 {
 	   statement2;
 	 }
 	else if (expression3)
 	 {
 	   statement3;
 	 }

Here, statement1 will be executed if expression1 is TRUE, statement2 will be executed if expression2 is TRUE and if none of the expressions are true then statement3 will be executed.

Note: Syntax error is detected by the compiler whereas logic error has its effect at execution time.