Create a structure that contains a pointer to an array - c++

Question

I CAN NOT USE VECTORS FOR THE ASSIGNMENT
I have to create a structure that stores the following information: student name, id number, pointer to an array of test scores, average test score, letter grade.
The program should keep a list of test scores for a group of students. It should ask the user how many students are in the class and how many test scores there are.The number of test scores will be the same for every student. The program should dynamically allocate an array of structures. Each structures Tests member should point to a dynamically allocated array which will hold the test scores.
After the arrays have been dynamically allocated, the program should ask the user for the id number and all of the test scores for each student. The average score should be calculated and stored in the Average member of the structure. Display the student info.
I am having trouble when the user enters the test scores in the inputScores function. I can't figure out how to access the structure member right. Can you please look at my code and help me figure out what I'm doing wrong?
Here is my structure:
struct Grade
{
string name;
int idNum;
int* tests;
double average;
char grade;
};
Here are my functions:
//user enters number of students which is then used as the size of the dynamically allocated struct array
int inputStudents();
//user enters number of tests for each student which is then used as the size of the dynamically allocated array of test scores in the structure
int inputTests();
string inputName();
int inputID();
//user inputs scores for each student. this is a function i'm struggling with
int *inputScores(int *testScores, int numTests);
double calcAvg(int *testScores, int numTests);
char calcGrade(double);
void display(Grade*, int);
Here is my main:
int main()
{
Grade *studentList;
int size = inputStudents();
studentList = new Grade[size]; //dynamically create array of Grade struct
int numTests = inputTests(); //number of test scores stored in numTests
for (int i = 0; i < size; i++) //loop to store all student's info
{
studentList[i].name = inputName();
studentList[i].idNum = inputID();
studentList[i].tests = inputScores(studentList[i].tests, numTests, i);
studentList[i].average = calcAvg(studentList[i].tests, numTests);
studentList[i].grade = calcGrade(studentList[i].average);
}
display(studentList, size);
delete[] studentList;
return 0;
}
Here is the function i am struggling with. Every time I reference studentList a different error appears. My program won't even compile and I'm pretty sure this function is the reason why. Here I pass the tests structure member, rather than the entire structure. I also pass the number of tests and the counter from the loop in main that tells us which student the user is entering the test scores for.
int *inputScores(int *studentList, int numTests, int count)
{
cout << endl;
cout << "Enter the test scores:\n";
for (int i = 0; i < numTests; i++)
{
studentList[count].tests = new int[numTests]; //my error says the studentList must have a class type
cout << "Score " << (i + 1) << ": ";
cin >> studentList[count]->tests[i]; //my error says studentList must have a pointer type
cout << endl;
}
return studentList->tests; //my error says studentList must have a point-to-class type
}

Answer 1

You are passing a pointer to each student's test array to inputScores() but accessing it as a pointer to a student. You would have to change the inputScores() function as given below:
void inputScores(int *tests, int numTests, int count)
{
cout << endl;
cout << "Enter the test scores:\n";
for (int i = 0; i < numTests; i++)
{
cout << "Score " << (i + 1) << ": ";
cin >> tests[i];
cout << endl;
}
}
Also, I made one more modification. Its always better if the caller function allocates memory and pass a reference to the array. So we need to call the inputScores() function as given below
studentList[i].tests = new int[numTests];
inputScores(studentList[i].tests, numTests, i);
This is the output I received:
How many students are there?
3
How many tests does each student have?
2
Enter the student's name:
Joohn
Enter the student's ID number:
1
Enter the test scores:
Score 1: 12
Score 2: 13
Enter the student's name:
Jack
Enter the student's ID number:
2
Enter the test scores:
Score 1: 67
Score 2: 45
Enter the student's name:
Jill
Enter the student's ID number:
3
Enter the test scores:
Score 1: 56
Score 2: 89
--------------------------------------------------------
Here is all the info I have for each student:
Student #1:
Name: Joohn
ID Number: 1
Test Scores: Average Grade: 12
Letter Grade: F
Student #2:
Name: Jack
ID Number: 2
Test Scores: Average Grade: 56
Letter Grade: F
Student #3:
Name: Jill
ID Number: 3
Test Scores: Average Grade: 72
Letter Grade: C
--------------------------------------------------------

Answer 2

Your function inputScores is declared like this
int *inputScores(int *studentList, int numTests, int count)
which means studentList is a pointer to an int (which can be treated like an array). Later in the function, you attempt to do this:
studentList[count].tests = new int[numTests];
If studentList is an int* (or int array), then studentList[count] is just an int. You're trying to access the member variable tests of an int. But int is a primitive type.
When you called this function in main, you correctly passed an int*:
studentList[i].tests = inputScores(studentList[i].tests, numTests, i);
So treating the variable like it were actually an int * instead of a Grade * should solve the first of your problems. You should also change the name of the variable, since you're not really passing a studentList, it's more of a tests variable. That should help cut down on some of the confusion.
int *inputScores(int *tests, int numTests, int count)
After that, you'll realize that even through you're passing studentList[i].tests to your inputScores function, you'll have a memory leak and not be able to access the memory you thought you just filled. You DID fill memory, but when you tried to assign a new value to tests via tests = new int[numTests];, that only changed the local copy of tests.
To fix THAT problem, you need to pass tests by reference, like this:
int *inputScores(int*& tests, int numTests, int count)
That will allow any changes you make in your function to the int*, tests, to persist outside of the function.