Write a C program to check whether a given number is an Armstrong number or not.

Article by: Manish Methani

Last Updated: September 26, 2021 at 2:04pm IST
2 min 45 sec

An Armstrong number is a number that equals the sum of the cube of each digit in a number. 

For example, suppose a given number is 153. 

To check whether a given number is Armstrong or not, we have to take the cube of each digit in a number and take a sum of those.

153 = (1*1*1) + (5*5*5) + (3*3*3)

After the addition of the cube of each digit, we get the original number which is 153. Hence, the given number is Armstrong.

#include <stdio.h>
int main()
{
   int n = 153, sum = 0, remainder = 0,tempNumber;
   tempNumber = n;
   while(tempNumber!=0)
   {
      remainder = tempNumber % 10;
      sum = sum + (remainder*remainder*remainder);
      tempNumber /= 10;
   }

   if(sum==n)
   {
     printf("%d is an Armstrong number.",n);
   }
   else
   {
     printf("%d is not an Armstrong number.",n);
   }
   return 0;
  }

Output

153 is an Armstrong number

Program Logic

1. First, we take the original number into a temporary variable which is tempNumber.
2. Then, we get the last digit of a temporary number using the modulo method inside a loop.
3. After getting the last digit of a number, we added it with the cube of that last digit number.
4. Then assigned the remaining digits except for the last digit of a number using the Quotient method.
5. This process will be in the loop till we find that givenNumber do not reach 0.

If at the end we find that this new number after addition is found as. same or not. If yes, then the given number is an Armstrong number else it is not an Armstrong number.

C Program to check whether a given number is Armstrong or not using a user-defined function

#include <stdio.h> 
int isArmstrong(int n)
{
  int tempNumber=n;
  int remainder,sum;
  sum=0;
  while(tempNumber!=0)
  {
    remainder=tempNumber%10;
    sum = sum + (remainder*remainder*remainder);
    tempNumber/=10;
  }

if(sum==n) 
   return 1
else
   return 0;
}

int main()
{
  int n = 153;
  if(isArmstrong(n))
      printf("%d is an Armstrong number.",n);
  else
      printf("%d is not an Armstrong number.",n);
  return 0;
}

Output

153 is an Armstrong number