大整数加法C++（计蒜客）

#include <iostream>
#include<string>
using namespace std;
int main()
{
    string str1,str2;
    cin >> str1 >> str2;//保存两个数字
    int d = 0;//进位
    int str3[210];
    int i = 0;
    int a, b;
    for (;i < str1.length() ||i< str2.length();++i)
    {
        if (i >= str1.length())
        {
            a = 0;
       }
        else   a = str1[str1.length() - 1 - i] - (int)‘0‘;
        if (i >= str2.length())
        {
            b = 0;
        }else b = str2[str2.length() - 1 - i] - (int)‘0‘;
        int c = a + b+d;
        if (c >= 10) d = 1;
        else d = 0;
        str3[i] = c%10;
    }
    if (d == 1)
    {
        str3[i] = 1;
        i++;
    }
    bool flag = 0;//判断第一个数是不是0
    for (int j = i-1;j >=0;--j)
    {
        if (str3[j] != 0 || flag)
        {
            flag = 1;
            cout << str3[j];
        }
       
    }
    if (!flag) cout << 0;//这点千万不能忘记
    return 0;
}