Factorial Calculation Upto 1000!

#define NUM  1002
#define SIZE 2585
#include<stdio.h>
#include<string>
using namespace std;


char fact[NUM + 1][SIZE], num[5];
void character_multiplication(char *num1, char *num2, char *result)
{
int i, j, k, index, carry, mul, length1, length2;


length1 = strlen(num1);
length2 = strlen(num2);
//Assign all elements of 'result' of length 'length1 + length2' with '0'.
j = length1 + length2;


for(i = 0; i < j; i++) result[i] = '0';
index = -1;


//Take one digit from 'num2' one by one.
for(i = length2 - 1; i > -1; i--)
{
index++;  carry = 0;


//Multiply each digit of 'num1' by the digit taken from 'num2'.
for(j = length1 - 1, k = index; j > -1; j--, k++)
{
mul = (num1[j] - '0') * (num2[i] - '0') + (result[k] - '0') + carry;
carry = mul / 10;
result[k] = mul % 10 + '0';
}
result[k] = carry % 10 + '0';
}


//If the last carry is not '0' then keep it in result.
if (carry != 0) ++k;


result[k] = NULL;
reverse(&result[0],&result[k]);
return;
}




int main()
{
int i, number;


strcpy(fact[0], "1");
for(i = 1; i <= NUM; i++)
{
sprintf(num, "%d", i);
character_multiplication(fact[i - 1], num, fact[i]);
}
while(scanf(" %d", &number) == 1)
printf("%d!\n%s\n", number, fact[number]);


return 0;
}
/*
Input:
15
24
9
Output:
15!
1307674368000
24!
620448401733239439360000
9!
362880
*/