PENGKODINGAN C++ MENGHITUNG NILAI

#include <cstdlib>
#include <iostream>

using namespace std;

class Nilai

{
      public:
             Nilai();
             void input();
             void output();
             private:
                     int a,b,c,n;
                     };
      Nilai::Nilai()
      {
                    cout<<"fergie erlanda";
                    cout<<endl;
      }
      void Nilai::input()
      {
           cout<<"masukan nilai A : ";cin>>a;
           cout<<"masukan nilai B: ";cin>>b;
           cout<<"masukan nilai c : ";cin>>c;
           }
           void Nilai::output()
           {    n=(a+b+c)/3;
                if(a>=80 && n<=100)
                {cout<<"Nilai A";}
                else if(n>=65 && n<80)
                {cout<<"nilai B";}
                else if(n>=55 && n<65)
                {cout<<"nilai C";}
                else if(n>=30&&n<55)
                {cout<<"nilai D";}
                else
                {cout<<"Gak lulus";}
                cout<<endl;
                }
      int main(int argc, char *argv[]){
          Nilai n;
          n.input();
          n.output();
         
    system("PAUSE");
    return EXIT_SUCCESS;
}


Di coba masbro !!