if else in C program

If( test expression ) 
Statement block if TRUE

If( test expression ) 
{
Statement block if condition TRUE
}else{
Statement block if condition  False 	
}

Nested if else

#include <stdio.h>
int main(void){
int num1;
	printf("Enter the  number ");
scanf("%d",&num1);  // Enter  numbers
if(num1 <= 10)
{
printf(" Your number is less than or equal to ten");
}
else
{
printf(" Your number is more than ten"); // printng outputs
 }
return 0;
}

Example of nested if else

#include <stdio.h>
int main(void){
int num;
	printf("Enter a number less then or equal to 100 :  ");
	scanf("%d",&num);
	
	if(num >= 80)
        printf(" First Division  " );
	else {
		if(num>= 60){
		printf(" Second Division ");
		}else{
		  if( num>=40){
		  printf(" Third Division ");
		  }else{
		  printf(" Fail ");
		  }
		}
	}
return 0;
}

Using else if

if(expression is true){
 // statement to execute	
}
else if ( expression is true){
 // statement to execute	
}else if ( expression is true){
 // statement to execute	
}
else {
// final statement to execute if nothing is ture	
}

int main()
{
int x=20;

if(x>=30){
  printf(" I am greater than or equal to 30  \n");
}else if(x<20){
  printf(" I am less than 20 \n");
}else 
  printf("I am greate than or equal to 20  but less than 30 \n");
}

Example 1: Basic if-else Statement

This example demonstrates how to use a simple if-else statement to check if a number is positive or negative.

#include <stdio.h>

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    
    if (num >= 0) {
        printf("%d is positive.\n", num);
    } else {
        printf("%d is negative.\n", num);
    }
    
    return 0;
}

Enter a number: 5
5 is positive.

Example 2: if-else if-else Ladder

This example shows how to use if-else if-else to categorize an age.

#include <stdio.h>

int main() {
    int age;
    printf("Enter your age: ");
    scanf("%d", &age);
    
    if (age < 13) {
        printf("You are a child.\n");
    } else if (age < 20) {
        printf("You are a teenager.\n");
    } else if (age < 60) {
        printf("You are an adult.\n");
    } else {
        printf("You are a senior citizen.\n");
    }
    
    return 0;
}

Enter your age: 25
You are an adult.

Example 3: Nested if-else Statements

This example demonstrates using nested if-else statements to check for even or odd numbers.

#include <stdio.h>

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    
    if (num >= 0) {
        if (num % 2 == 0) {
            printf("%d is an even number.\n", num);
        } else {
            printf("%d is an odd number.\n", num);
        }
    } else {
        printf("The number is negative.\n");
    }
    
    return 0;
}

Enter a number: 12
12 is an even number.