Gradebook Reader

#include <iostream>
#include <iomanip>
#include <fstream>
using namespace std;

int main()
{
    ifstream gradebook("grades.txt");
    int a, b, c, d, f;
    double per, t, i;
    char data;
    a = 0;
    b = 0;
    c = 0;
    d = 0;
    f = 0;
    i = 0;
    t = 0;
    if(gradebook.is_open())
    {
        while(!gradebook.eof())
        {
            gradebook >> data;
            if(data == 'A')
            {
                a += 1;
            }
            else if(data == 'B')
            {
                b += 1;
            }
            else if(data == 'C')
            {
                c += 1;
            }
            else if(data == 'D')
            {
                d += 1;
            }
            else if(data == 'F')
            {
                f += 1;
            }
            else
            {
                i += 1;
            }
        }
    }
    gradebook.close();
    t = a + b + c + d + f + i;
    system("cls");
    cout << "A's: " << a << "\n";
    cout << "B's: " << b << "\n";
    cout << "C's: " << c << "\n";
    cout << "D's: " << d << "\n";
    cout << "F's: " << f << "\n";
    cout << "Invalid data: " << i << "\n";
    per = i / t * 100;
    cout << "Percent of Invalid Data: " << setprecision(2) << per << "%\n\n";
    system("pause");
    return(0);
}