代码

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

const int MAXN = 10005;
int a[MAXN], b[MAXN];
int c[MAXN * 2];

int read(int *a) {
	static char buf[MAXN];
	scanf("%s", buf);
	int n = strlen(buf);
	for (int i = 0; i < n; i++) {
		a[n - 1 - i] = buf[i] - 48;
	}
	return n;
}

int main() {
	int n_a = read(a), n_b = read(b);
	for (int i = 0; i < n_a; i++) {
		for (int j = 0; j < n_b; j++) {
			c[i] += a[i] * b[j];
		}
	}
	for (int i = 0; i < n_a + n_b; i++) {
		c[i + 1] += c[i] / 10;
		c[i] = c[i] % 10;
	}
	int i;
	for (i = n_a + n_b; i; i--) {
		if (c[i]) break;
	}
	for (; i >= 0; i--) {
		putchar(c[i] + 48);
	}
}

评测结果