1074 宇宙无敌加法器 （20 分）

#include <bits/stdc++.h>
using namespace std;
int main()
{
    string a,b,c;
    cin>>c>>a>>b;
    reverse(a.begin(),a.end());
    reverse(b.begin(),b.end());
    reverse(c.begin(),c.end());
    string s;

    int up=0,sum,k;
    while(a.length()!=b.length())
    {
        if(a.length()>b.length())
            b += '0';
        else
            a += '0';
    }
    for(int i=0;i<a.length();i++)
    {
        sum = a[i]-'0'+b[i]-'0'+up;
        if(i>c.length()-1 || c[i]=='0')
            k=10;
        else
            k=c[i]-'0';
        up = sum/k;
        sum %= k;
        s = (char)(sum + '0') + s;
    }
    if(up > 0)
        s = (char)(up + '0') + s;
    int count = 0;
    while(s[count] == '0' && s.length() > 1)
        s.erase(count, 1);
    cout<<s<<endl;
    return 0;
}