Armstrong number in C using function

In this post, you will learn how to write a C program to check whether a given number is Armstrong or not using a function.

A number is called an Armstrong number if the sum of its cubes of digits is equal to the number itself. It is also known as the Narcissistic number. To lay it out simply, assuming we have a 3-digit number, each of the digits is raised to the power of three and added to get a number. If the number obtained equals the original number, we call that an Armstrong number.

In number theory, we can say that an Armstrong number in a given number base b is a number that is the sum of its own digits, each raised to the power of the number of digits.

Formula to check Armstrong number

A positive number of n digits is called an Armstrong number of order n.

abcde.... = aⁿ + bⁿ + cⁿ + dⁿ + eⁿ +

The following example demonstrates why 371 is an Armstrong number.

371 = (3*3*3)+(7*7*7)+(1*1*1)  
where:   
(3*3*3)=27  
(7*7*7)=343 
(1*1*1)=1  
So:  
27+343+1 = 371

C program to check Armstrong number using function

In the given C program, we take input from the user and store it in a variable called num. Next, we define a custom function armstrong() and pass the entered value in argument. Next, we split all the digits of the num and calculate the cube value of the digits. Then, we add all cube values together and save the output to the variable sum. If the sum equals the num, then the num is an Armstrong number; if the sum is not equal to num, then the num is not an Armstrong number.

We call this a custom function in our main function. If the custom function returns 0, then the entered number is an Armstrong number.

// Armstrong Number in C Using Function
#include<stdio.h>
int armstrong(int orgnum){
    int remainder = 0;
    int sum = 0;
    int power = 0;
    
    int num = orgnum;
    while (num != 0){
        // remainder contains the last digit
        remainder = num % 10;
        power = remainder * remainder * remainder;
        sum = sum + power;
        
        num = num / 10;
    }
    if (sum == orgnum)
        return 0;
    else
        return 1;
}

int main(){
    int num;
    
    // getting input from user
    // and store in a variable
    printf("Enter a number: ");
    scanf("%d", &num);
    
    if (armstrong(num) == 0){
        printf("%d is an Armstrong Number.", num);
    }
    else{
        printf("%d is not an Armstrong Number.", num);
    }
    return 0;
}

Output of the above code:

Enter a number: 371
371 is an Armstrong Number.

Enter a number: 252
252 is not an Armstrong Number.

Enter a number: 153
153 is an Armstrong Number.

C program to check Armstrong number of n digits using function

In the given C program, we check the armstrong number of n digits using a custom function.

// Armstrong Number in C Using Function
#include <stdio.h>
int armstrong(int orgnum){
    int remainder = 0;
    int sum = 0;
    int num,n = 0;
    float result = 0.0;

    num = orgnum;

    for (num = orgnum; num != 0; ++n) {
       num /= 10;
    }

    for (num = orgnum; num != 0; num /= 10) {
       remainder = num % 10;

      // store the sum of the power 
      // of individual digits in result
      result += pow(remainder, n);
    }

    // if num is equal to result, 
    // the number is an Armstrong number
    if ((int)result == orgnum)
     return 0;
    else
     return 1;
}

int main(){
    int num;
    
    // getting input from user
    // and store in a variable
    printf("Enter a number: ");
    scanf("%d", &num);
    
    if (armstrong(num) == 0){
        printf("%d is an Armstrong Number.", num);
    }
    else{
        printf("%d is not an Armstrong Number.", num);
    }
    return 0;
}

Output of the above code:

Enter a number: 1634
1634 is an Armstrong Number.

Enter a number: 4150
4150 is not an Armstrong Number.

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