Ndtyjky

I have a vector std::vector<StudentGradeInfo> gradebook; objects of the class StudentGradeInfo. The StudentGradeInfo class contains the following member variables:
std::string studentName;
int studentID;
std::string major;

What I need to do is overload the == operator to compare the ID input from the user and compare it to the studentID member variables of the objects in the vector std::vector<StudentGradeInfo> gradebook;.

How would I go about looping through the vector to compare the ID's? It would probably be a non-member function since it is comparing an int variable to a member function of an object, but I do not know how to do this.

I guess you could do it like this if you absolutely have to make an overloaded operator==.

bool operator==(const StudentGradeInfo& sgi, int id) {

    return sgi.studentID == id; 

}



std::vector<StudentGradeInfo> gradebook;

int id_to_find=1234;



for(auto& sgi : gradebook) {

    if(sgi==id_to_find) {

        //...

    } 

}

I suppose you want to loop through the vector to find a studentGrandeInfo-object with a particular ID. You can accomplish this rather easy by using std::find_if together with a lambda-function for the proper comparison. The code could look as follows:

int toFind = 4219; // some ID

auto it = std::find_if(

gradebook.begin(), gradebook.end(),

[&toFind](const StudentGradeInfo& x) { return x.studentID == toFind;});

In your case, as you the studentID seems to serve as a "unique key", I'd use data structure std::map<int, StrudentGradeInfo> instead.

Overloading operator == is - as gsamars pointed out - somehow impractical, as it is meant for comparing two objects of the same type (and not an object with an int). See the following code illustrating this:

struct StudentGradeInfo {

    std::string studentName;

    int studentID;



    bool operator==(const StudentGradeInfo& c) const {

        return c.studentID == studentID;

    }

};



int main() {



    std::vector<StudentGradeInfo> gradebook {

        { "john", 123 },

        { "max", 345 }

    };



    StudentGradeInfo aNewOne { "sepp", 345 };

    auto it = find(gradebook.begin(),gradebook.end(),aNewOne);

    if (it == gradebook.end()) {

        cout << "345 does not exist" << endl;

    } else {

        cout << "345 already exists" << endl;

    }



}