字符串表示的大整数相乘

题目要求：

设计一大整数相乘的函数，函数原型int multiply(char *strNum1,char *strNum2, char *strRslt)，strNum1是字符串表示的被乘数，strNum2是字符串表示的乘数，strRslt用来存放乘积结果的字符串。

例如：strNum1 = “2345678901234”；
        strNum2 = "23456789"

乘积结果，strRslt="55022095047997777626"

函数实现：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int multiply(char *strNum1,char *strNum2, char *strRslt) 
{  
    int i,j,carry,t,tt;  
    int len1, len2;
    int rslt_index = 0;
    if(strNum1 == NULL || strNum2 == NULL || strRslt == NULL)
        return -1;
    len1 = strlen(strNum1);
    len2 = strlen(strNum2);
    memset(strRslt, 0 ,len1+len2);//把存放结果的空间先清零
    for(i = 0; i < len2; i++)  
    {  
        carry = 0;  
        for(j = 0; j < len1; j++)  
        {      
            t = (strNum1[len1-1-j]-'0')*(strNum2[len2-1-i]-'0')+carry;//从最低位开始计算  
              if(0 == t)
                continue;                  
            rslt_index = j+i;          
            tt = strRslt[rslt_index] + t;      
            strRslt[rslt_index] = tt % 10;      
            carry = tt / 10;  
        }  
        if(carry > 0)
        {  
            strRslt[++rslt_index] += carry;  
        }  
    }
    //反串
    for(i = 0; i <=rslt_index/2; i++)
    {
        t = strRslt[i] + '0';
        strRslt[i] = strRslt[rslt_index-i] + '0';
        strRslt[rslt_index-i] = t;
    } 
    return 0;
}  

int main(void)
{
    char a[20] = {0}; 
    char b[20] = {0}; 
    char result[50] = {0}; 
    
    printf("Pls input first integer:");
    scanf("%s",a);
    printf("Pls input second integer:");
    scanf("%s",b);
    multiply(a, b, result);
    printf("result is:%s
",result);
    return 0;
}