Struggling with dynamically allocating an array within a class

[ngeisler]

I am attempting to create three different students using three different constructors and getting a error codes LNK2019 and LNK 1120.
It may have something to do with me attempting to dynamically allocate an array to hold test scores.
The only functions I have only shown the main function as well as the functions involving the dynamically allocated array
Any help would be appreciated!

  void makeArray()//Private class member that creates dynamically allocated array
		{
			test = new int[num];
			for(int count = 0; count < num; count++)
			{
				test[count] = 0;
			}
		}

//Constructors, public class members
		Student()
		{
			setName("None");
			setID(10);
			num = 3;
			makeArray();
		}
		Student(int n)
		{
			setName("None");
			setID(10);
			if(n > 0)
			{
				num = n;
			}
			else
			{
				num=3;
			}
			makeArray();
		}		
		Student(string nm, int i, int n)
		{
			nm = "None";
			setName(nm);
			i = 10;
			setID(i);
			if(n>0)
			{
				num = n;
			}
			else
			{
				num = 3;
			}
			makeArray();
		}

//public class member functions that use the array
		void setScore(int i, int s)
		{
			if(0 <= i <= num && 0<=s<=100)
			{
				test[i] = s;
			}
			else
			{
				cout << "Cannot set test " << i+1 << 
"to " << s <<" for " <<getName() << "\n";
			}
		}
void showScore()
		{
			for(int count = 0; count < num; count++)
			{
				cout << "Test " << count+1 << " had a score of " << test[count] << "\n";
			}
		}

int main() //main function
{
	Student A();
	Student B(4);
	Student C("Joe", 40, 5);

	A().setName("Tom");
	A().setID(200);
	A().setID(20);
	A().setScore(0, 75);
	A().setScore(1, 85);
	A().setScore(2, 95);

	B.setName("John");
	B.setID(30);
	B.setScore(0, 70);
	B.setScore(1, 80);
	B.setScore(2, 90);
	B.setScore(3, 100);
	
	C.setScore(0, 90);
	C.setScore(1, 91);
	C.setScore(2, 92);
	C.setScore(3, 93);
	C.setScore(4, 94);
	C.setScore(5, 95);
	C.setScore(4, 105);
	C.setScore(-5, -105);

	A().display();
	B.display();
	C.display();
	system("Pause");
	return 0;
}

Sorry for the wall of code!

[LB]

The linker error numbers are not helpful. Please copy and paste the exact error message that you are getting.

Usually linker errors are because you defined something 0 times (e.g. forgot to define it) or more than 1 times (e.g. two or more definitions, even if they are the same). Everything in a program must be defined exactly once.

[ngeisler]

error LNK2019: unresolved external symbol "class Student __cdecl A(void)" (?A@@YA?AVStudent@@XZ) referenced in function _main

and

error LNK1120: 1 unresolved externals

I also am getting 3 warnings

Edit:
The three warnings are about the use of <=,
I'm not sure if they are actually important

[LB]

Aha, I see it now. On line 3 of your main function snippet, you have this:

Student A();

This is a common mistake that goes unnoticed due to something called Most Vexing Parse. What happens is, this line ends up declaring a function named A which takes no parameters and returns a Student by value. To fix it, remove the parenthesis:

Student A;

Lines 7-12 looks like you were getting an error and you decided to fix it by not thinking about why you weren't getting errors for B and C.

[ngeisler]

Thanks! I appreciate the help, I've got it at least running.
Now my problem is getting my error messages, such as the one in the function setScore, to work properly.

[LB]

if(0 <= i <= num && 0<=s<=100)

You cannot write conditions that way. You have to do this instead:

if(0 <= i && i <= num && 0 <= s && s <= 100)