大数乘法

#include
#include
#include
using namespace std;
int str1[100], str2[100], res[100];
int len1, len2, len3;
void setData(){
	string s1, s2;
	cin >> s1 >> s2;
	reverse(s1.begin(), s1.end()); reverse(s2.begin(), s2.end());
	len1 = s1.size(); len2 = s2.size();
	int i = 0;
	for (auto x : s1) str1[i++] = x - ‘0‘;
	i = 0;
	for (auto x : s2) str2[i++] = x - ‘0‘;	
}
void example(){
	for (int i = 0; i < 10; i++) {
		str1[i] = str2[i] = i;
	}
	len1 = len2 = 10;
}
void show(){
	for (int i = len3; i >= 0; i--)
		cout << res[i];
}
void calc(int len1,int len2){
	len3 = max(len1, len2)-1;//相应自始至终都不进位的情形
	for (int i = 0; i < len2; i++){
		for (int j = 0; j < len1; j++){
			res[i + j] += str2[i] * str1[j];
			if (res[i + j] >= 10){
				len3 = max(len3, i + j + 1);
				res[i + j + 1] += res[i + j] / 10;
				res[i + j] %= 10;
			}
		}
	}
}
int main(){
	setData();
	//example();
	calc(len1,len2);
	show();
	getchar(); getchar();
	return 0;

}
/*
9876543210*9876543210=97546105778997104100
*/