题解 | #高精度整数加法#

#include <iostream>
#include <algorithm>
#include <string>

using namespace std;

string sumString(string& num1,string &num2)
{
    string smaller = num1.size()>num2.size()? num2:num1;
    string bigger = num1.size()>num2.size()? num1:num2;
    int last = 0;
    reverse(smaller.begin(),smaller.end());
    reverse(bigger.begin(),bigger.end());
    //从最低位置进行增加
    string result;
    for(int i = 0;i!=smaller.size();++i)
    {
        int n1 = static_cast<int>(smaller[i]-'0');
        int n2 = static_cast<int>(bigger[i]-'0');
        n2 += (n1+last);
        if(n2>9)
        {
            result.push_back(static_cast<char>(n2-10+'0'));
            last = 1;
        }
        else
        {
            result.push_back(static_cast<char>(n2+'0'));
            last = 0;
        }
    }
    for(int i = smaller.size();i!=bigger.size();++i)
    {
        int n1 = static_cast<int>(bigger[i]-'0');
        n1+=last;
        if(n1>9)
        {
            result.push_back(static_cast<char>(n1+'0'-10));
            last = 1;
        }
        else {
            result.push_back(static_cast<char>(n1+'0'));
            last = 0;
        }
    }
    if(last!=0)
        result.push_back(static_cast<char>(1+'0'));
    reverse(result.begin(), result.end());
    return result;
}

int main() {
    string num1;
    string num2;
    getline(cin, num1);
    getline(cin,num2);
    cout<<sumString(num1, num2);
}
// 64 位输出请用 printf("%lld")

反向处理，然后从后到前