[05/30/13] Challenge #126 [Intermediate] Perfect P'th Powers - http://www.reddit.com/r/dailyprogrammer/comments/1fcpnx/053013_challenge_126_intermediate_perfect_pth/

Perfect-Pth-Powers.c

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

void usage(char *argv0);
unsigned char isPrime(unsigned long num);

int main(int argc, char *argv[])
{
    unsigned long input = 0, result = 0;
    unsigned long base = 0, exponent = 0;

    if (argc != 2)
    {
        usage(argv[0]);
        exit(1);
    }

    input = strtoul(argv[1], NULL, 0);

    if (isPrime(input))
    {
        printf("1 (%lu^1)\n", input);
        return 1;
    }

    for (base = 1;base<input/2;base++)
    {
        for(exponent = 1;exponent<input;exponent++)
        {
            result = (unsigned long)pow((double)base, (double)exponent);
            if (result == input)
                break;
        }
        if (result == input)
            break;
    }

    printf("%lu (%lu^%lu)\n", exponent, base, exponent);

}

/**
 * Print usage infomation in command line.
 * @param argv0 The name of the executable
 */
void usage(char *argv0)
{
    printf("Usage: %s [number]\n", argv0);
    return;
}

/**
 * Check if a number is prime.
 * @param num The number to check if prime.
 */
unsigned char isPrime(unsigned long num)
{
    unsigned long i = 0;

    if (num <= 1)
        return 0;

    if (num == 2)
        return 1;

    if (!(num % 2) || !(num % 3) || !(num % 5) || !(num % 7))
        return 0;

    for (i = 11;i<num;i++)
        if (!(num % i))
            return 0;

    return 1;
}