Armstrong number: An n-digit number equal to the sum of the n-th powers of its digits.

armstrong_number.c

#include <math.h>

int is_armstrong_number(int x)
{
    int i = 0, c_pow = 0, sum = 0;
    int digit = x;
    int module = x;

    while(digit != 0) {
        digit /= 10;
        c_pow++;
    }
    digit = x;
    while(i++ < c_pow) {
        digit %= 10;
        sum += pow((double)digit, c_pow);
        module /= 10;
        digit = module;
    }

    return (x == sum);
}