一堆变量正在取消初始化.不知道该怎么办

需要帮助弄清楚为什么会发生这个错误，我觉得我只是掌握了一些函数和数组。这个问题应该把最多100个等级读入一个数组，计算平均值，找到最高等级，然后找到最低等级。我相信你们只要看代码就能知道。我只是输入剩下的内容，以便能够满足发布代码所需的要求。

-编辑：我想回答所有帮助我解决这个问题的人。我解决了这个问题，从答案中学到了很多东西。现在，我遇到的问题就是弄清楚如何正确地取出最高的数组和最低的数组。我应该能够弄清楚这一点，你们都给了我很大的帮助，我非常感激！

// This program will read in a group of test scores( positive integers from 1 to 100)
// from the keyboard and then calculates and outputs  the average score
// as well as the highest and lowest score. There will be a maximum of 100 scores.
// PLACE YOUR NAME HERE
#include <iostream>
using namespace std;
typedef int GradeType[100];  // declares a new data type: 
                             // an integer array of 100 elements

float findAverage (const GradeType, int);  // finds average of all grades
int   findHighest (const GradeType, int);  // finds highest of all grades
int   findLowest  (const GradeType, int);  // finds lowest of all grades
int main()
{
    GradeType  grades;                     // the array holding the grades.
    int  numberOfGrades;                   // the number of grades read.
    int pos;                               // index to the array.
    float avgOfGrades;                     // contains the average of the grades.
    int highestGrade;                      // contains the highest grade.
    int lowestGrade;                       // contains the lowest grade.
    // Read in the values into the array
    pos = 0;
    cout << "Please input a grade from 1 to 100, (or -99 to stop)" << endl;
    cin  >> grades[pos];
    while (grades[pos] != -99)
    {
        pos++;
        cin >> grades[pos];
    }
    numberOfGrades = pos;  // Fill blank with appropriate identifier
    // call to the function to find average
    avgOfGrades = findAverage(grades, numberOfGrades);
    cout << endl << "The average of all the grades is " << avgOfGrades << endl;

    findHighest (grades, numberOfGrades);//  Fill in the call to the function that calculates highest grade

    cout << endl << "The highest grade is " << highestGrade << endl;

    findLowest (grades, numberOfGrades);// Fill in the call to the function that calculates lowest grade
   cout << "n The lowest grade is n" << lowestGrade<< "/n"; // Fill in code to write the lowest to the screen
    return 0;
}
//****************************************************************************
//                                 findAverage
//
// task:          This function receives an array of integers and its size.
//                It finds and returns the average of the numbers in the array
// data in:       array of floating point numbers
// data returned: avarage of the numbers in the array
//
//****************************************************************************
float findAverage (const GradeType  array, int size)
{  
    float sum = 0;   // holds the sum of all the numbers
    for (int pos = 0; pos < size; pos++)

       sum = sum + array[pos];
    return (sum / size);  //returns the average
}
//****************************************************************************
//                                 findHighest
//
// task:          This function receives an array of integers and its size.
//                It finds and returns the highest value of the numbers in
//                the array
// data in:       array of floating point numbers
// data returned: highest value of the numbers in the array
//
//****************************************************************************
int   findHighest (const GradeType array, int size)
{
    float highestgrade;
    for (int pos = 0; pos < size; pos++)
        if(array[pos]>highestgrade)
            {
                highestgrade= array[pos];
        }
        return highestgrade;
   // Fill in the code for this function
}

//****************************************************************************
//                                 findLowest
//
// task:          This function receives an array of integers and its size.
//                It finds and returns the lowest value of the numbers in 
//                the array
// data in:       array of floating point numbers
// data returned: lowest value of the numbers in the array
//
//****************************************************************************
int   findLowest  (const GradeType array, int size)
{
   float lowestgrade;
   for (int pos =0; pos > size; pos++)
       if(array[pos] < lowestgrade)
           {
               lowestgrade=array[pos];
              // Fill in the code for this function
       }
return lowestgrade;
}