Largest product in a series

gistfile1.c

// https://projecteuler.net/problem=8

#include <stdio.h>
#include <string.h>

#define MAX_DIGIT 13
#define NUM 1000

int main(void) {
	char num[NUM+1];
	strcat(num, "73167176531330624919225119674426574742355349194934");
	strcat(num, "96983520312774506326239578318016984801869478851843");
	strcat(num, "85861560789112949495459501737958331952853208805511");
	strcat(num, "12540698747158523863050715693290963295227443043557");
	strcat(num, "66896648950445244523161731856403098711121722383113");
	strcat(num, "62229893423380308135336276614282806444486645238749");
	strcat(num, "30358907296290491560440772390713810515859307960866");
	strcat(num, "70172427121883998797908792274921901699720888093776");
	strcat(num, "65727333001053367881220235421809751254540594752243");
	strcat(num, "52584907711670556013604839586446706324415722155397");
	strcat(num, "53697817977846174064955149290862569321978468622482");
	strcat(num, "83972241375657056057490261407972968652414535100474");
	strcat(num, "82166370484403199890008895243450658541227588666881");
	strcat(num, "16427171479924442928230863465674813919123162824586");
	strcat(num, "17866458359124566529476545682848912883142607690042");
	strcat(num, "24219022671055626321111109370544217506941658960408");
	strcat(num, "07198403850962455444362981230987879927244284909188");
	strcat(num, "84580156166097919133875499200524063689912560717606");
	strcat(num, "05886116467109405077541002256983155200055935729725");
	strcat(num, "71636269561882670428252483600823257530420752963450");
	
	int i,start,end;
	unsigned long long temp, product = 0;
	for(start = 0, end = MAX_DIGIT; end < NUM; start++, end++ )
	{
		temp = 1;
		for(i = start; i<end;++i)
		{
			temp *= num[i] - '0';
		}
		if (temp > product) 
		{			
			product = temp;
		}
	}
	printf("%llu", product);
	return 0;
}