面试题---两个大整数相乘

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

void reverse(char *value)
{
    int len = strlen(value);
    char *p = value;
    char *q = value + len - 1;
    while(p < q)
    {
        *p ^= *q;
        *q ^= *p;
        *p ^= *q;
        p++;
        q--;
    }
}

void mult(char *num1,char *num2)
{
    int len1 = strlen(num1);
    int len2 = strlen(num2);
    int len3 = len1 + len2;

    char *result = (char *)malloc(len3 + 1);
    memset(result,'0',len3 + 1);
    int i = 0;
    for(i = 0;i < len3 - 1;i++)
    {
        int m = 0;
        int res = 0;
        for(m = 0;m <= i && m < len1;m++)
        {
            int n = 0;
            for(n = 0;n <= i && n < len2;n++)
            {
                if(m + n == i)
                {
                    int value1 = num1[m] - '0';
                    int value2 = num2[n] - '0';
                    res = res + value1 * value2;
                }
            }
        }
        res = res + result[i] - '0';
        result[i] = res % 10  + '0';
        result[i + 1] = res / 10 + '0';
    }

    reverse(result);
    printf("结果为：%s
",result);

}



int main()
{
    printf("输入第一个数：
");
    char num1[20];
    scanf("%s",num1);
    printf("输入第二个数：
");
    char num2[20];
    scanf("%s",num2);
    reverse(num1);
    reverse(num2);
    printf("逆序后为：%s,%s
",num1,num2);
    mult(num1,num2);
    return 0;
}