Error: EXC BAD ACCESS C++.. Debugged my code can't find anything wrong with it. Please take a look

For some reason it is not computing the quiz grade at all.

#include<iostream>
#include<string>
class StudentInfo{
private: //Private variables
    double quiz1;
    double quiz2;
    double midterm;
    double final;
    double average;
    char Grade_Letter;
    double StudentNumber;


public: // public member functions
    void input(StudentInfo& student);
    void computeGrade(StudentInfo& student);
    void output(const StudentInfo student);

};

using namespace std;
int main(){
    int class_size;
     StudentInfo student[class_size];
    cout<<"How many Students do you want to Average";

    cin>>class_size;
    // Variable delcaration of type structure

    // Forloop to call function to read the details of each student
    for(int i = 0; i<class_size;i++){
        student[i].input(student[i]);
    }
        for(int i = 0; i<class_size;i++){

            // Function to call the grade of each student
            student[i].computeGrade(student[i]);
            student[i].output(student[i]);
            cout<<endl;;
        }
        }
    void StudentInfo:: input(StudentInfo& student){
    //Getting info
    //Inputing student number
    cout<<"Enter Student Number"<<endl;
    cin>>student.StudentNumber;
    //inputing midterm grade
    cout<<"Enter Midterm grade";
    cin>>student.midterm;
    cout<<"Enter 2 quiz grades, max 10 point each";
    cin>>student.quiz1>>student.quiz2;
    if(student.quiz1>10 || student.quiz2>10){
        cout<<"Score to high, remember max score is 10.";
    }
    cout<<"Enter Final grade"<<endl;
    cin>>student.final;
}
void StudentInfo :: computeGrade(StudentInfo& student){
    // Quiz Average
    double quizAvg= (student.quiz1 + student.quiz2)/2.0;
    double quizAvg2 = quizAvg * 10;
    student.average = student.final * .5 + student.midterm * .25 + quizAvg2 * .25;
    char grade_letter = 'F';
    if(student.average <= 50 && student.average){
        grade_letter = 'F';
    }
    if(student.average <= 70 && student.average >= 60){
        grade_letter = 'D';
    }
    if(student.average <= 80 && student.average >= 70){
        grade_letter = 'C';
    }
    if(student.average <= 90 && student.average >= 80){
        grade_letter = 'B';
    }
    if(student.average >= 90){
        grade_letter = 'A';
    }
    student.Grade_Letter = grade_letter;
}
void StudentInfo:: output(const StudentInfo student){
    cout<< "Quiz Grades are:"
    << student.quiz1<<" " << student.quiz2<<" "
    <<endl;
    cout<<" Midterm Grade is:"<<student.midterm<<endl;
    cout<<"Final Grade is:"<<student.final<<endl;
    cout<<"your Grade letter is:"<<student.Grade_Letter<<endl;
}

OUTPUT:

How many Students do you want to Average1
Enter Student Number
1
Enter Midterm grade90
Enter 2 quiz grades, max 10 point each9
9
Enter Final grade
90

Then the program suddenly stops in the compute member function