30分求大佬看看

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
using namespace std;
string a,b;
int n;
int c[2001];
string s(string x)
{    string d;
    d=x;
    int len=x.size();
    for(int i=0;i<len;i++)
    {
        if(x[len-1-i]<='9'&&x[len-1-i]>='0')
            d[i]=x[len-1-i];
        else d[i]=x[len-1-i]-7;
    }    
    return d;
}
int main()
{
    cin>>n;
    cin>>a>>b;
    a=s(a);
    b=s(b);
    //cout<<a<<endl<<b;
    int len=a.size();
    int len1=b.size();
    len=max(len,len1);
    for(int i=0;i<len;i++)
    {
        c[i]+=b[i]-'0'+a[i]-'0';
        //cout<<c[i]<<endl;
        if(c[i]>=n)
        {
        c[i]-=n;
        c[i+1]+=1;
        }
    }int i;
    for(i=len+2;c[i]==0;--i);
    for(;i>=0;i--)
    {
        if(c[i]>=10)
        {    char x=c[i]-10+'A';
            cout<<x;
        }
        else cout<<c[i];
    }
}