C++ calculation and character issue

[DossarLX ODI]

I just started getting into C++; this is a simple assignment but there's something about calculations and even a character issue here that I can't figure out.

The catch of the assignment is to input quiz grades for a student, input the weight the quiz has on the total grade, calculate the student's final grade by getting the average, and then assigning a letter grade (this is the character part).

class Student
{
    
public:           
    void input();
    void output();	

private:
    int qgrade[4]; // Each array cell indicates the quiz number's grade.
    int qweight[4]; // Each array cell indicates the quiz number's weight.
    // 0 for quiz1, 1 for quiz2, 2 for midterm, 3 for final exam.
    double avweight;
    char lettergrade;

    double calc_ave();
    char calc_letter();

};

My input function also calls the calc_ave and calc_letter functions to assign a letter grade and final average for that student. The inputs themselves work, but then I have these lines of code and this is when things get screwy.

Student::avweight = calc_ave();
Student::lettergrade = calc_letter();

avweight comes out to be something stupid like 2800 or something, and then lettergrade just doesn't appear at all (it's a blank space where there should be a letter). I'll show the functions so I can make any appropriate corrections concerning what may have gone wrong.

double Student::calc_ave(){
    
    int i;
    double total = 0.0;
    for ( i = 0 ; i < 4 ; i++ )
    {
        total += (double)( Student::qgrade[i] * Student::qweight[i] );
    }
    return total;
}

char Student::calc_letter(){
    double avgrade = Student::avweight;
    char lgrade; // For storing the letter grade to return
    if( avgrade < 65.0 )
        lgrade = 'F';
    else if( avgrade >= 65.0 && avgrade < 70.0 )
        lgrade = 'D';
    else if( avgrade >= 70.0 && avgrade < 80.0 )
        lgrade = 'C';
    else if( avgrade >= 80.0 && avgrade < 90.0 )
        lgrade = 'B';
    else if( avgrade >= 90.0 && avgrade <= 100.0 )
        lgrade = 'A';
    return lgrade;
}

So basically the inputs for the student work, but when I call the calc_ave and calc_letter functions, I print out the values and the letter grade comes up as a blank space while calc_ave gives some number that is way off.

EDIT: Here's sample output to show what I'm talking about

Please input student 1's grades.
Grades and weight should be input out of 100.
Input grade for quiz #1: 80
Input weight for quiz #1: 20
You entered 80 and 20
Input grade for quiz #2: 70
Input weight for quiz #2: 20
You entered 70 and 20
Input grade for midterm exam: 60
Input weight for midterm exam: 25
You entered 60 and 25
Input grade for final exam: 75
Input weight for final exam: 35
You entered 75 and 35
7125Average weight.
  letter grade.
Student 1's grades successfully entered.

Student Grade Evaluator
This program enters grades for 3 students and calculates them.
0 - Quit Program
1 - Input Grades
2 - Output Grades
Please select an item from the menu list: 2
Student 1's grades are:
Quiz 1: 80
Quiz 2: 70
Miderm Exam: 60
Final Exam: 75
This student scored 7125 and got a  for the course.

80 x .2
70 x .2
60 x .25
75 x .35

16 + 14 + 15 + 26.25 = 71.25

It should say the student got a grade of 71.25 and a letter grade of C, but that's not what's happening here.

[arcnmx]

Re: C++ calculation and character issue

Input grade for quiz #1: 80
Input weight for quiz #1: 20
total += (double)( Student::qgrade[i] * Student::qweight[i] );

Your types are integers, so that would be doing 80*20 rather than 80*0.2

Your letter isn't appearing since the grade is over 100, and you don't assign anything to lgrade in that case (so it'll default to junk / a meaningless character).

[DossarLX ODI]

Re: C++ calculation and character issue

Ok, so I asked the weights to be entered as integers. I forgot to divide by 100.0 when multiplying them in the calc_ave function.

Since the numbers were too large, it went out of the boundaries of the calc_letter numbers. Thanks arcnmx! I'll test it out again.

Edit: That works. I thought I somehow didn't get the character assignment syntax correct or something. I was getting junk values before I assigned sizes to the arrays as well.