Error passing data through c++ function

Hi I am having an error while running the code below. When I try to find the grade average, the data is not passed properly through the function. I am not sure where I am getting the error, but when I utilize the findGradeAverage function it leads to a negative number error that does not print out properly when I run it. I don't really understand how I get this error, as much as I would like a solution for this school assignment I would like to understand the nature of this problem and how I created it as well so I don't run into this problem in the future. Thanks.

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

const   int MAXGRADE = 25;              // maximum number of grades per student 
const   int MAXCHAR = 30;               // maximum characters used in a name

typedef char StringType30[MAXCHAR + 1]; // character array data type for names
                                    // having 30 characters or less.

typedef float GradeType[MAXGRADE];      // one dimensional integer array data type

float findGradeAvg(GradeType, int);     // finds grade average by taking array of
                                    // grades and number of grades as parameters

char findLetterGrade(float);            // finds letter grade from average given
                                    // to it as a parameter 
int main()
{
    StringType30 firstname, lastname;   // two arrays of characters defined
    int numOfGrades;                    // holds the number of grades
    GradeType grades;                   // grades defined as a one dimensional array
    float average;                      // holds the average of a student's grade
    char moreInput;                     // determines if there is more input

    cout << setprecision(2) << fixed << showpoint;

    // Input the number of grades for each student
    cout << "Please input the number of grades each student will receive." << endl
         << "This must be a number between 1 and " << MAXGRADE << " inclusive"
         << endl;
    cin >> numOfGrades;

    while (numOfGrades > MAXGRADE || numOfGrades < 1)
      {
          cout << "Please input the number of grades for each student." << endl
          << "This must be a number between 1 and " << MAXGRADE
          << " inclusive\n";
          cin >> numOfGrades;
      }

      // Input names and grades for each student
     cout << "Please input a y if you want to input more students"
          << " any other character will stop the input" << endl;
     cin >> moreInput;

     while (moreInput == 'y' || moreInput == 'Y')
       {
          cout << "Please input the first name of the student" << endl;
          cin >> firstname;

          cout << endl << "Please input the last name of the student" << endl;
          cin >> lastname;

          for (int count = 0; count < numOfGrades; count++)
            {
               cout << endl << "Please input a grade" << endl;

               cin >> grades[numOfGrades];  // Fill in the input statement to place grade in the array
        .   }

    cout << firstname << " " << lastname << " has an average of ";

    cout << findGradeAvg(grades, numOfGrades);// Fill in code to get and print average of student to screen

    cout << "Which results in a grade of " << endl;

    average = findGradeAvg(grades, numOfGrades);

    cout << findLetterGrade(average);   // Fill in call to get and print letter grade of student to screen

    cout << endl << endl << endl;

    cout << "Please input a y if you want to input more students"
        << " any other character will stop the input" << endl;
    cin >> moreInput;
}

 return 0;
}

//***********************************************************************
// findGradeAvg
//
// task:          This function finds the average of the
//                numbers stored in an array.
//
// data in:       an array of integer numbers
// data returned: the average of all numbers in the array
//
//***********************************************************************

float findGradeAvg(GradeType array, int numGrades)
{
    float average = 0.0;
    int total = 0;
    for (int count = 0; count < numGrades; count++)
      {
        total += array[count];
        average = total / numGrades;
      }
    return average;
}

//***********************************************************************
// findLetterGrade
//
// task:          This function finds the letter grade for the number
//                passed to it by the calling function
//
// data in:       a floating point number
// data returned: the grade (based on a 10 point spread) based on the 
//                number passed to the function
//
//***********************************************************************

char findLetterGrade(float numGrade)
{
    char letter;

    if (numGrade >= 90 && numGrade <= 100)
        letter = 'A';
    else if (numGrade >= 80 && numGrade <= 89)
        letter = 'B';
    else if (numGrade >= 70 && numGrade <= 79)
        letter = 'C';
    else if (numGrade >= 60 && numGrade <= 69)
        letter = 'D';
    else
        letter = 'F';

    return letter;
}