if-else-if Statement (Ladder) in C with Examples

In programming, if-else-if statement is also known as if-else-if ladder. It is used when there are more than two possible action based on different conditions.

Syntax

General syntax for if-else-if statement is:

if (Condition1)
{
     Statement1;
}
else if(Condition2)
{
     Statement2;
}
.
.
.
else if(ConditionN)
{
     StatementN;
}
else
{
     Default_Statement;
}

Working

In the above syntax of if-else-if, if the Condition1 is TRUE then the Statement1 will be executed and control goes to next statement in the program following if-else-if ladder.

If Condition1 is FALSE then Condition2 will be checked, if Condition2 is TRUE then Statement2 will be executed and control goes to next statement in the program following if-else-if ladder.

Similarly, if Condition2 is FALSE then next condition will be checked and the process continues.

If all the conditions in the if-else-if ladder are evaluated to FALSE, then Default_Statement will be executed.

The working of if-else-if ladder can be illustrated by following flowchart:

Flowchart

Programming Examples

Example 1: C program to find largest from three numbers given by user to explain working of if-else-if statement or ladder

#include<stdio.h>

int main()
{
	 int a,b,c;
	 printf("Enter three numbers: \n");
	 scanf("%d%d%d", &a, &b, &c);
	 if(a>b && a>c)
	 {
	  	printf("Largest = %d", a);
	 }
	 else if(b>a && b>c)
	 {
	  	printf("Largest = %d", b);
	 }
	 else
	 {
	  	printf("Largest = %d", c);
	 }
	 return(0);
}

Output

Run 1:
-------------
Enter three numbers: 
12 ↲
33 ↲
-17 ↲
Largest = 33

Run 2:
-------------
Enter three numbers: 
-18 ↲
-31 ↲
-17 ↲
Largest = -17

Run 3:
-------------
Enter three numbers: 
118 ↲
19 ↲
-87 ↲
Largest = 118

Note: ↲ indicates enter is pressed.

Explanation

During the first run i.e. Run 1, numbers given by user are 12, 33, and -17 respectively. These numbers are stored in variable a, b and c i.e. a gets 12, b gets 33 and c gets -17. In the if-else-if ladder first condition is a>b && a>c. So, what happens here? Lets break this condition!

Putting values of a, b and c condition becomes 12>33 && 12>-17, Right? In the first part of condition, we have 12>33. This is checking, is 12 greater than 33? Answer is NO. So, 12>33 evaluates to FALSE. Similarly, In the second part of condition, we have 12>-17. This is checking, is 12 greater than -17? Answer is YES. So, 12>-17 evaluates to TRUE. Results of these two conditions are combined by logical AND opeartor. So, finally FALSE && TRUE is evaluated. Since logical AND opeartors gives FALSE when one of the operand is FALSE, so FALSE && TRUE evaluates to FALSE.

When condition in if is FALSE then it prevents execution of printf("Largest = %d", a); and checks for another condition. Another condition here is b>a && b>c. Which is 33>12 && 33>-17 and evaluates to TRUE && TRUE, which in turn evaluates to TRUE. So b>a && b>c evaluates to TRUE and hence printf("Largest = %d", b); is executed printing Largest = 33. And then execution goes to next statement neglecting else block where it executes retun(0) which is the last statement in the program and program execution comes to end.

Example 2: C program to print weekday based on given number.

#include<stdio.h>
	
int main()
{
	 int day;
	 printf("Enter day number: ");
	 scanf("%d", &day);
	 if(day==1)
	 {
	  	printf("SUNDAY.");
	 }
	 else if(day==2)
	 {
	  	printf("MONDAY.");
	 }
	 else if(day==3)
	 {
	  	printf("TUESDAY.");
	 }
	 else if(day==4)
	 {
	  	printf("WEDNESDAY.");
	 }
	 else if(day==5)
	 {
	  	printf("THURSDAY.");
	 }
	 else if(day==6)
	 {
	  	printf("FRIDAY.");
	 }
	 else if(day==7)
	 {
	  	printf("SATURDAY.");
	 }
	 else
	 {
	  	printf("INVALID DAY.");
	 }
	 return(0);
}

Output:

Run 1:
-------------
Enter day number: 4↲
WEDNESDAY.

Run 2:
-------------
Enter day number: 2↲
MONDAY.

Run 3:
-------------
Enter day number: 10↲
INVALID DAY.

Run 4:
-------------
Enter day number: -1↲
INVALID DAY.

Note: ↲ indicates enter is pressed.

Example 3: C program to find largest number from four given numbers.

#include<stdio.h>
	
int main()
{
	 float a,b,c,d, lg;
	 printf("Enter four numbers:\n");
	 scanf("%f%f%f%f", &a, &b, &c, &d);
	
	 if(a>b && a>c && a>d)
	 {
	  	lg = a;
	 }
	 else if(b>a && b>c && b>d)
	 {
	  	lg = b;
	 }
	 else if(c>a && c>b && c>d)
	 {
	  	lg = c;
	 }
	 else
	 {
	  	lg = d;
	 }
	 printf("Largest = %f", lg);
	 return(0);
}

Output

Run 1:
-------------
Enter four numbers:
21.4↲
54.4↲
34.5↲
-67.5↲
Largest = 54.400000

Note: ↲ indicates enter is pressed.