forward declaration of class does not work

[Shahrin]

#include<iostre am>
using namespace std;

class teacher;

class student
{
int dept;

public:


student(int d)
{
dept=d;
}

bool TsameDept (teacher tch)
{
if (dept==tch.getD ept())
return true;
else
return false;
}
};

class teacher
{
int dept;

public:

teacher(int d)
{
dept=d;
}
int getDept()
{
return dept;
}
};




void main()
{
student st(5);
teacher tch(5);

if (st.TsameDept(t ch)==true)
cout<<"Same";

else cout<<"Differen t";
}

can anybody pls help

why this program shows compile error------use of undefined type 'teacher' or left of '.getDept' must have class/struct/union type

though I forward declared the teacher class.

[weaknessforcats]

You can only use a forward reference for a pointer to a class object.

That is, this code:

class MyClass;

is sufficient for the compiler to allow:

MyClass* ptr;

Anything beyond that you will be required to supply the class definition.

[Banfa]

You can use them for references to

MyClass& ref;

What you can't do is use it o declare an object or access any member of the class.