Variable is not a type

Question

#include<iostream>
#include<string>
#include<vector>
using namespace std;
class Course
{
    public:
        string name;
        string instructorInCharge;
        int numberOfStudents;
        int totalMarks;
        Course(string u, string v, int p, int q){
            this->name=u;
            this->instructorInCharge=v;
            this->numberOfStudents=p;
            this->totalMarks=q;

        }
    
    vector<int> studentMarks (numberOfStudents);

    

};
class Labs:public Course
{
   
        vector<int>labMarks(numberOfStudents);

};

int main()
{
    Course c("Rahul","Hota",200,300);
    cout<<"hello there";
}

When I compile this code I’m getting the following error:

1.cpp:20:31: error: 'numberOfStudents' is not a type
   20 |     vector<int> studentMarks (numberOfStudents);
      |                               ^~~~~~~~~~~~~~~~
1.cpp:28:29: error: 'numberOfStudents' is not a type
   28 |         vector<int>labMarks(numberOfStudents);
      |                             ^~~~~~~~~~~~~~~~

Please tell me what my mistake is. numberostudents was supposed to be the size of the vector. But not any function.

Answer 1

If you want in-class initialization, you may do this:

vector<int> studentMarks = vector<int>(numberOfStudents);

Now the default constructor will initialize studentMarks with vector<int>(numberOfStudents) when an instance of Course is created.

However, this will cause undefined behavior since numberOfStudents is not initialized before the initialization of studentMarks. You could use the member initalizer list instead:

Course(std::string u, std::string v, int p, int q)
    : name(std::move(u)),
      instructorInCharge(std::move(v)),
      numberOfStudents(p),
      totalMarks(q),
      studentMarks(numberOfStudents)
{
}

and likewise for the Labs class:

class Labs : public Course {
public:
    Labs(std::string u, std::string v, int p, int q)
        : Course(u, v, p, q),  // initialize the base class part of a `Labs`
          labMarks(p)          // initialize the added member variable
    {
    }
    std::vector<int> labMarks;
};