50分求助！！！

#include <bits/stdc++.h>
using namespace std;
string n1;
int ans=0,a[1001],b[1001],c[1001],m,n[1001],a1[1001],b1[1001],tmp;
int main() {
    cin>>m>>n1;
    for (int i = n1.length() - 1, j = 0; i >= 0; i--, j++){
        n[i]=n1[j]-'0';
    }
    for (int i = n1.length() - 1, j = 0; i >= 0; i--, j++){
        a1[i]=n[i];
        b1[i]=n[j];
        if(a1[i]!=b1[i]){
            tmp++;
        }
    }
    for(int x=1;x<=30;x++){
        if(tmp==0){
            if(ans!=0){
                ans++;
            }
            cout<<"STEP="<<ans;
            return 0;
        }
        tmp=0;
        for (int i = n1.length() - 1, j = 0; i >= 0; i--, j++){
            a[i]= n[i];
            b[i]=n[j];
        }
        for (int i = 0; i < n1.length(); i++) {
            c[i] += a[i] + b[i];
            c[i + 1] = c[i] / m;//模拟进位
            c[i] %= m;
            n[i]=c[i];
        }
        for (int i = 0; i < n1.length(); i++) {
            c[i]=0;
        }
        for (int i = n1.length() - 1, j = 0; i >= 0; i--, j++){
            a1[i]=n[i];
            b1[i]=n[j];
            if(a1[i]!=b1[i]){
                tmp++;
            }
        }
        ans++;

    }
    cout<<"Impossible!";
    return 0;
}

哪里不对？