C Programming Code Examples

C > For Loops and While Loops Code Examples

Program to find Armstrong numbers in given range



Program to find Armstrong numbers in given range

What is Armstrong number?

An Armstrong number is a n-digit number that is equal to the sum of nth power of its digits. For example,
371 = 3^3 + 7^3 + 1^3 = 371
407 = 4^3 + 0^3 + 7^3 = 407

Logic to find all Armstrong number between 1 to n

    Input upper limit to print Armstrong number from user. Store it in some variable say end.
    Run a loop from 1 to end, increment 1 in each iteration. The loop structure should look like for(i=1; i<=end; i++).
    Inside the loop print current number i, if it is Armstrong number.

#include <stdio.h>
#include <math.h>

int main()
{
    int j, lastDigit, digits, sum, i;
    int start, end;

    /* Input lower and upper limit from user */
    printf("Enter lower limit: ");
    scanf("%d", &start);
    printf("Enter upper limit: ");
    scanf("%d", &end);

    printf("Armstrong number between %d to %d are: \n", start, end);

    for(i=start; i<=end; i++)
    {
        sum = 0;

        /* Copy the value of j for processing */
        j = i;

        /* Find total digits in j */
        digits = (int) log10(j) + 1;

        /* Calculate sum of power of digits */
        while(j > 0)
        {
            /* Extract the last digit */
            lastDigit = j % 10;

            /* Find sum of power of digits */
            sum = sum + pow(lastDigit, digits);

            /* Remove the last digit */
            j = j / 10;
        }

        /* Check for Armstrong number */
        if(i == sum)
        {
            printf("%d, ", i);
        }
    }

    return 0;
}