大数相乘

#include "stdafx.h"
#include <stdio.h>
#include <string.h>
#include <conio.h>
#define LEN 1000
void mult(char [],char [],char []);
main(){    
	char op1[LEN],op2[LEN],op3[LEN*2-1];    
	scanf("%s%s",op1,op2);    
	mult(op1,op2,op3);    
	printf("%s\n",op3);    
	getch();    
	return 0;   
}    
void reverse(char a[]){
	int longth=strlen(a);    
	int i;    
	for(i=0;i<longth/2;i++){        
		char t;        
		t=a[i];        
		a[i]=a[longth-i-1];        
		a[longth-i-1]=t;}
}
void mult(char op1[LEN],char op2[LEN],char ans[LEN*2-1]){    
	char top1[LEN];    
	char top2[LEN];    
	strcpy(top1,op1);    
	strcpy(top2,op2);    
	reverse(top1);    
	reverse(top2);    
	int k;    
	int top1s=strlen(top1);    
	int top2s=strlen(top2);    
	for(k=0;k<top1s+top2s;k++){        
		ans[k]='0';}    
	int i,j;    
	int jw,ys;    
	int longth;    
	for(j=0;j<top2s;j++){        
		jw=0;        
		for(i=0;i<top1s;i++){            
			ys=((top1[i]-'0')*(top2[j]-'0')+jw+ans[i+j]-'0')%10;            
			jw=((top1[i]-'0')*(top2[j]-'0')+jw+ans[i+j]-'0')/10;            
			ans[i+j]=ys+'0'; }        
		if(jw>0){            
			ans[i+j]=jw+'0'; }    
	}    
	longth=i+j-1;    
	if(jw>0)        
		ans[longth++]=jw+'0';    
	ans[longth]='\0';    
	reverse(ans);}