WhyCan Forum(哇酷开发者社区)

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

char* real_mult(const char* a, const char* b) {
	int i, j, k, m, n, len_a, len_b;
	len_a = strlen(a);
	len_b = strlen(b);
	int* res_p;
	char* c;
	res_p = (int*)malloc((len_a + len_b) * sizeof(int));
	if (!res_p) {
        printf((const char*)"malloc int[%d] fail!\n", len_a + len_b);
        for ( ; ; );
	}
	for (i = len_a + len_b - 1; i >= 0; i--) {
		res_p[i] = 0;
	}
	for (i = 0; i < len_a; i++) {
		for (j = 0; j < len_b; j++) {
			k = i + j + 1;
			res_p[k] += (a[i] - '0') * (b[j] - '0');
		}
	}
	res_p[0] = 0;
	for ( ; k > 0; k--) {
		res_p[k - 1] += res_p[k] / 10;
		res_p[k] %= 10;
	}
	for (j = 0; j < len_a + len_b; j++) {
        if (res_p[j] != 0) {
            break;
        }
	}
	c = (char*)malloc((len_a + len_b + 1 - j) * sizeof(char));
	if (!c) {
        printf((const char*)"malloc char[%d] fail!\n", len_a + len_b + 1 - j);
        for ( ; ; );
	}
	for (i = 0; i < len_a + len_b - j; i++) {
		c[i] = (char)(res_p[i + j] + '0');
	}
	free(res_p);
	c[i] = '\0';
	return c;
}

char* mult1(char* a, const char* b) {
    char* c = real_mult((const char*)a, b);
    free(a);
    return c;
}

char* order(int n) {
    char temp[16];
    char* res = (char*)"1";
    for ( ; n > 1; n--) {
        sprintf((char*)temp, "%d", n);
        res = mult1(res, (const char*)temp);
    }
    return res;
}

int main(int argc, const char* argv[]) {
    char* c;
    c = order(20000);
    printf("%s\n", c);
    free(c);
    return 0;
}