c++大数相乘

懒得多说，直接上代码

#include <iostream>
#include <string>
#include <vector>
using namespace std;

 

vector<int> str_to_vec(const string &str)
{
    vector<int> ivec;
   
    for (int i = str.size()-1; i >= 0; i--)
    {
        ivec.push_back(static_cast<int>(str[i] - '0'));
    }
   
    return ivec;
}

string operator *(const string &lhs, const string &rhs)
{
    const int lhs_size = lhs.size();
    const int rhs_size = rhs.size();
    vector<int> ivec_lhs = str_to_vec(lhs);
    vector<int> ivec_rhs = str_to_vec(rhs);
    vector<int> ivec_result(lhs_size+rhs_size, 0);
   
    for (int i = 0; i < lhs_size; i++)
    {
        int k = i;
        for (int j = 0; j < rhs_size; j++, k++)
        {
            ivec_result[k] += ivec_lhs[i] * ivec_rhs[j];
        }
    }
   
    for (vector<int>::iterator iter = ivec_result.begin(); iter != ivec_result.end(); iter++)
    {
        if (*iter > 9)
        {
            *(iter+1) += *iter/10;
            *iter %= 10;
        }
    }
   
    vector<int>::iterator iter = ivec_result.end()-1;
    while (*iter == 0)
    {
        ivec_result.pop_back();
        iter = ivec_result.end()-1;
    }
   
    string str_result;
    while (!ivec_result.empty())
    {
        char c = static_cast<char>(ivec_result.back()) + '0';
        str_result.append(1, c);
        ivec_result.pop_back();
    }
   
    return str_result;
}

 

int main()
{
    string str_multiplicand;
    string str_multiplier;
    string str_result;

    cout<<"Input the multiplicand:"<<endl;
    cin>>str_multiplicand;
    cout<<"Input the multiplier:"<<endl;
    cin>>str_multiplier;

    str_result = str_multiplicand * str_multiplicand;
    cout<<str_multiplicand<<"*"<<str_multiplier<<"="<<str_result<<endl;

    return 0;
}