大整数乘法C++

//大整数乘法

#include <bits/stdc++.h>

using namespace std;

int na[2005], nb[2005], nc[4010];

string mul(string a, string b) {

int lena = a.size();

int lenb = b.size();

for (int i = 0; i < lena; i++)

na[lena - i] = a[i] - '0';

for (int i = 0; i < lenb; i++)

nb[lenb - i] = b[i] - '0';

int lenc = lena + lenb;

for (int i = 1; i <= lena; i++)

for (int j = 1; j <= lenb; j++) {

nc[i + j - 1] += na[i] * nb[j];

nc[i + j] += nc[i + j - 1] / 10;

nc[i + j - 1] = nc[i + j - 1] % 10;

}

while (nc[lenc] == 0 && lenc > 0)

lenc--;

string ans;

for (int i = lenc; i >= 1; i--) {

ans += nc[i] + '0';

}

return ans;

}

int main() {

string a, b;

cin >> a >> b;

cout << mul(a, b) << endl;

return 0;

}