高精度乘法

#include<bits/stdc++.h> 
const int N = 2e4+9;
int a[N];
int b[N];
int c[N];
using namespace std;
int main(){
	string str1;
	string str2;
	cin>>str1>>str2;
	int len1 = str1.size();
	int len2 = str2.size();
//	if(str1 == "0"||str2 == "0")
//	{
//		cout<<"0";
//		return 0;
//	}
//	cout<<"len1 "<<len1<<endl;
//	cout<<"len2 "<<len2<<endl;
	for(int i =1,j = len1 - 1;i<=len1;++i,--j)
	{
		a[i] = str1[j]-'0';
	}
	for(int i =1,j = len2 - 1;i<=len2;++i,--j)
	{
		b[i] = str2[j]-'0';
	}
//	for(int i =1;i<=len1;++i)
//	{
//		cout<<a[i]<<" ";
//	}
//	cout<<endl;
//	for(int j =1;j<=len2;++j)
//	{
//		cout<<b[j]<<' '; 
//	}
	for(int i = 1;i<=len1;++i)
	{
		for(int j = 1;j<=len2;++j)
		{
		//	cout<<"a[i]*b[j]  "<<a[i]*b[j]<<endl; 
			c[i+j - 1] =(a[i] * b[j] )+c[i+j-1] ;
			c[i+j] = c[i+j - 1]/10 + c[i+j];
			c[i+j - 1] = c[i+j - 1]%10;
		//	cout<<i+j-1<<" " <<c[i+j - 1]<<endl;
		//	cout<<i+j<<" "<<c[i+j]<<endl;
		}
	}
	while(c[len1+len2] == 0&& len1+len2 > 1) {
		len1--;	
		//cout<<len1+len2<<endl; 
	}
//	cout<<len1+len2<<endl;
	for(int i =len1+len2;i >= 1;--i)
	{
		cout<<c[i];
	}
	return 0;
}