C – If, If-else and Nested If-else Statements

If Statement

For Decision making, C uses the keyword if. The general form of the if statement is

if(text_expression)
statement1;

The test expression should always be enclosed in parentheses. If the test_expression is nonzero(true) then the statement statement1 is executed; Otherwise, statement1 is skipped and control passes to the next statement. Statement1 can be a single statement or compound statement.

The statement1 part of the if statement is the body of the if statement. This construct is shown in the following flowchart. 

C Code

#include<stdio.h>
int main(void){
     int marks;
        printf("Enter Marks :");
        scanf("%d",&marks);
             if(marks>=40)
                 printf("Passed");
      return 0;
}

C Output

Enter Marks: 50
Passed

If -Else Statement

The if – else statement is also used for decision making purpose, C uses the keyword if-else. The general form of the if-else statement is,

if(test_expression)
 statement1;
else 
 statement2;

The if statement executes a single statement or a compound statement, when the test expression is true or nonzero. It does nothing when the test expression is not true.

When the test expression is true or nonzero, then the body of if is executed and control passes to the next statement immediately following the if-else construct. But if the expression is not true or zero then the body of else is executed.

C Code

#include<stdio.h>
int main(void)
{
 int g;
 printf("Enter Your Marksn");
 scanf("%d",&g);
 if (g>=60)
  printf("you passedn");
 else
  printf("you failedn");
}

C – Output

Condition1;
Enter Your Marks
45
you failed   Condition 2;

Enter Your Marks
61
you passed 

Nested If-Else Statement

The meaning of nesting is to have same construct within itself. Nesting means statement inside statement. Previously we learn about if-else statement, we identified a set of statements as the if block ans another set as the else block.

The statement within the if-else statements could be another if or if-else statement. So this type of statement is called a nested conditional statement. This inner conditional expression is said to be nested within the outer one.

C Code

if(expression 1)
 if(expresssion2)
  statement1;
 else
  statement2;
else
  if(expresssion2)
  statement3;
 else
  statement4;

  The statements can be surrounded by compound statement, if there exist more than one statement or other statement.

C Code

#include<stdio>
int main(void){
 int n,v;
 printf("Enter 2 Numbers:");
 scanf("%d%d",&n,&v);
 if(n>v)
  printf("first is larger");
 else
  if(n<v)
   printf("second is largern");
  else
   printf("both numbers are equaln");
  return 0;
}