i need help with this assignment

i have this class and i need to implement the functions and the main

i've implemented it but i want to check if its right

and i have a problem in writing the main

```
#ifndef
#define
class GBook
{
public:
GBook();
void inputGrades();
void setCourseNo(long x);
long getCourseNo()const;
void displayMsg();
int max(int x1,int x2,int x3);
void displayReport();
private:
long CourseNo;
int MaxValue;
};
#endif
//functions implementation
//function to input 3 grades
void GBook::inputGrades(int x1,int x2,int x3)
{
grade1=x1;
grade2=x2;
grade3=x3;
}
//constructor
GBook::GBook()
{
CourseNo=1001;
MaxValue=0;
}
//set function
void GBook::setCourseNo(long x)
{
CourseNo=x;
}
//get function
long GBook::getCourseNo()
{
return CourseNo;
}
/*function to display MSG and
to take course no from get function*/
void GBook::displayMsg()
{
cout<<"welcome in the course no ";
cout<<getCourseNo()<<endl;
}
//function to find max value from 3 values
int GBook::max(int x1,int x2,int x3)
{
max=x1;
if(x2>x1)
max=x2;
else if(x3>x2)
max=x3;
}
/*function to call all previous
funtions to be used in the main
void GBook::displayReport()
{
setCourseNo(x);
displayMsg();
inputGrades(x1,x2,x3);
max(x1,x2,x3);
}
//destructor
GBook::~GBook()
{
}
```

I have to write the main now and ask

the user to input 3 grades then call

only "displayReport" function not all the functions