求两个字符串的乘积，结果存到字符串中

求两个字符串的乘积，结果存到字符串中，例如字符串一中存的“657891”，字符串二中存的“521”，分别将字符串中的字符转换成整型数字，进行计算后，再转换成字符类型存储起来函数为         void mul（char *input1，int n，char *input2, int m，char *output）其中input1和input2是输入，n是input1的长度，n2是input2的长度。Output是输出

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

/**
*实现字符串的反转，ptrBegin和ptrEnd分别指向开始和结束的字符，不包括‘\0’
e.g.  原来的字符"1234"  ptrBegin指向‘1’， PtrEnd指向'4'
*/
void reversalStr(char *ptrBegin, char *ptrEnd){
	char temp;
	while(ptrBegin < ptrEnd){
		temp = *ptrBegin;
		*ptrBegin = *ptrEnd;
		*ptrEnd = temp;
		ptrBegin++;
		ptrEnd --;
	}
}
void intToStr(int data, char *str){
	int flag = 0;
    char *ptr = str;
	if(data < 0){
		flag = 1;
		data = -data;
	}
	if(data == 0){
		*str = '0';
		str ++;
	}
	while(data != 0){
		*str = data % 10 + '0';
		data /= 10;
		str++;
	}
	if(flag){
		*str = '-';//是负数的话，加个符号在末尾
		str++;
	}
	//字符反转
	reversalStr(ptr, str-1);
	*str = '\0';
}
int strToInt(char *str){
	int data = 0;
	const char *ptr = str;
	if(*str == '-'){
		str ++;
	}
	while(*str != '\0'){
		if(*str < '0' || *str > '9'){
			break;
		}
		data = data * 10 + (*str - '0');
		str ++;
	}
	if(*ptr == '-'){
		data =-data;
	}
	return data;
}
void mul(char *input1, int n, char *input2, int m, char *output){
	int num1, num2, result;
	num1 = strToInt(input1);
	num2 = strToInt(input2);
	printf("num1 = %d\tnum2 = %d\t\n", num1, num2);
	result = num1 * num2;
	printf("result = %d\n", result);
	intToStr(result, output);
}
void main(){
	char *str1 = "-357891";
	char *str2 = "-521";
	char outStr[50];
	mul(str1, strlen(str1), str2, strlen(str2), outStr);
	printf("%s\n", outStr);
	getchar();
}