C Program to Check Armstrong Number

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

A number is called an Armstrong number if the sum of cubes of every digit of a number is equal to the number itself.
For Example
407 is an Armstrong number
407 = 4*4*4 + 0*0*0 + 7*7*7

121 is not an Armstrong number
121 is not equal to 1*1*1 + 2*2*2 + 1*1*1

Examples of Armstrong Numbers : 0, 1, 2, 3, 153, 370, 407 etc.

Algorithm to check for Armstrong number

• Take a number as input from user and store it in an integer variable(Let’s call it inputNumber).
• Find the cubic sum of digits of inputNumber, and store it in sum variable.
• Compare inputNumber and sum.
• If both are equal then input number is Armstrong number otherwise not an Armstrong number..

C program to check a number is Armstrong number or not

This program first takes a number as input from user using scanf function and stores it in variable ‘number’. It makes a copy of number in variable ‘temp’. Then using a while loop, it calculates the cube of every digit of temp(loop will terminate when temp becomes zero) and stores in a ‘sum’ variable. If sum is equal to number then it is an Armstrong number otherwise not an Armstrong number.

/*
* C Program to check whether a number is armstrong number or not
*/
#include <stdio.h>
#include <conio.h>
 
int main(){
    int number, sum = 0, lastDigit, temp;
    printf("Enter a number : ");
    scanf("%d", &number);
    temp = number;
     
    while(temp != 0){
        lastDigit = temp%10;
        sum = sum + (lastDigit*lastDigit*lastDigit);
        temp = temp/10;
    }
     
    if(sum == number){
        printf("%d is Armstrong Number \n", number);
    } else {
        printf("%d is not an Armstrong Number \n", number);       
    }
    getch();
    return 0;
}

Program Output

Enter a number : 153
153 is Armstrong Number

Enter a number : 120
120 is not an Armstrong Number

C Program to check whether a number is Armstrong number or not using function

This program uses a user defined function getCubicSumOfDigits that returns the cubic sum of all digits of a number.

/*
* C Program to check whether a number is armstrong number or not
*/
#include <stdio.h>
#include <conio.h>
 
int getCubicSumOfDigits(int number);
int main(){
    int number, sum;
    printf("Enter a number \n");
    scanf("%d", &number);
     
    sum = getCubicSumOfDigits(number);
     
    if(sum == number){
        printf("%d is Armstrong Number \n", number);
    } else {
        printf("%d is not an Armstrong Number \n", number);       
    }
    getch();
    return 0;
}
 
/*
 * Funtion to calculate the sum of cubes of digits of a number
 * getCubicSumOfDigits(123) = 1*1*1 + 2*2*2 + 3*3*3;
 */
int getCubicSumOfDigits(int number){
    int lastDigit, sum = 0;
    while(number != 0){
        lastDigit = number%10;
        sum = sum + lastDigit*lastDigit*lastDigit;
        number = number/10;
    }
    return sum;
}

Program Output

Enter a number 407
407 is Armstrong Number