Scope and accessor functions with second constructors? - c++

Question

So basically my professor gave us the class student and told us to implement all functions and write a main for the function. I am trying to do this but I am having trouble figuring out the errors that are arising, in all of my accessor functions it is telling me that nCredits, gpa, and s aren't declared in the scope. I assume this has something to do with the second constructor, but I am not sure what exactly the issue is. The second constructor and the displayStRec function were also provided to our class, I just don't know how to do this program with the variables in the member function being renamed as they have been.
#include <iostream>
using namespace std;
class student
{
public:
student();
student(string s, double gpa, int nCredits);
~student(); //destructor
void changeCredits(int nCredits);
int getCredits();
void changeGPA(double gpa);
double getGPA();
void displayStRec();
private:
string name;
double GPA;
int credits;
};
student::student()
{
name = "No name yet";
GPA = 0;
credits = 0.0;
cout << "Default constructor entered!" << endl;
}
student::student(string s, double gpa, int nCredits)
{
name = s;
GPA = gpa;
credits = nCredits;
cout << "Second constructor entered!" << endl;
}
void student::changeCredits(int nCredits){
cout << "Enter credits earned:" << endl;
cin >> nCredits;
}
int student::getCredits(){
return nCredits;
}
void student::changeGPA(double gpa){
cout << "Enter GPA: " << endl;
cin >> gpa;
}
double student::getGPA(){
return gpa;
}
void student::displayStRec()
{
cout << " Name: " << s <<endl;
cout << " GPA: " << gpa <<endl;
cout << "Credits: " << nCredits <<endl;
}
student::~student()
{
cout << "Destructor entered!" << endl;
}
int main()
{
student s1,s2("John",4.0,42);
s2.changeCredits(nCredits);
s2.getCredits();
s2.changeGPA(gpa);
s2.getGPA();
s2.displayStRec();
return 0;
}

Answer 1

You've got three variables that you're using that aren't declared. I'll hit them one by one.
Missing s
void student::displayStRec()
{
cout << " Name: " << s <<endl;
cout << " GPA: " << gpa <<endl;
cout << "Credits: " << nCredits <<endl;
}
In this function, you are trying to output some variable s that isn't declared within the scope of displayStRec. You used s in the constructor to initialize the name, copying it to member variable name. Well, s is gone now! But name persists for the lifetime of the object. So, just use name instead.
void student::displayStRec()
{
cout << " Name: " << name <<endl; //Change it here
cout << " GPA: " << gpa <<endl;
cout << "Credits: " << nCredits <<endl;
}
Missing nCredits and gpa
In your main function you're using two variables that aren't declared.
int main()
{
student s1,s2("John",4.0,42);
s2.changeCredits(nCredits); //What nCredits?
s2.getCredits();
s2.changeGPA(gpa); //What gpa?
s2.getGPA();
s2.displayStRec();
return 0;
}
This leads to the question... what are you trying to change their credits to? What are you trying to change their gpa to? In other words, shouldn't your program have input parameters? Perhaps somewhere in your assignment your professor told you what values to provide. You will need constants of some kind, or you will need to gather user input from cin.
Oh and by the way, this makes zero sense
void student::changeGPA(double gpa){
cout << "Enter GPA: " << endl;
cin >> gpa;
}
This function will accept user input and update the variable gpa, which is declared in local scope and immediately discarded. Not very useful.
Also, it accepts an input value (double gpa) but also collects input from cin. Why do both? Can't update it to two values at the same time!
My guess is that is supposed to update the object's GPA, which is declared in member scope. Like this:
void student::changeGPA(){
cout << "Enter GPA: " << endl;
cin >> GPA;
}
or
void student::changeGPA(double gpa){
GPA = gpa;
}
Conclusion
One of the following must be true:
You copied the code examples incorrectly
The professor gave you a trick question
The professor is sort of clueless or perhaps a bit overworked

Answer 2

I've gone ahead and removed the sloppy second constructor functions my professor is trying to force on us and this program now works fine:
#include <iostream>
using namespace std;
class student
{
public:
student();
student(string s, double gpa, int nCredits);
~student(); //destructor
void changeCredits();
int getCredits();
void changeGPA();
double getGPA();
void displayStRec();
private:
string name;
double GPA;
int credits;
};
student::student()
{
name = "No name yet";
GPA = 0;
credits = 0.0;
cout << "Default constructor entered!" << endl;
}
student::student(string s, double gpa, int nCredits)
{
name = s;
GPA = gpa;
credits = nCredits;
cout << "Second constructor entered!" << endl;
}
void student::changeCredits(){
cout << "Enter credits earned: ";
cin >> credits;
}
int student::getCredits(){
return credits;
}
void student::changeGPA(){
cout << "Enter GPA: ";
cin >> GPA;
}
double student::getGPA(){
return GPA;
}
void student::displayStRec()
{
cout << " Name: " << name <<endl;
cout << " GPA: " << GPA <<endl;
cout << "Credits: " << credits <<endl;
}
student::~student()
{
cout << "Destructor entered!" << endl;
}
int main()
{
student s1,s2("John",4.0,42);
s2.changeCredits();
s2.getCredits();
s2.changeGPA();
s2.getGPA();
s2.displayStRec();
return 0;
}

Answer 3

here is a suggested solution however I don't know what your teacher orders:
!: add string to inclusion
2: use only member data not non members
3: either make changeCredits and changeGPA take 0 argument and inside it ask for inputs or input outside and and pass to it.
#include <iostream>
#include <string>
using namespace std;
class student
{
public:
student();
student(string s, double gpa, int nCredits);
~student(); //destructor
void changeCredits();
int getCredits();
void changeGPA();
double getGPA();
void displayStRec();
private:
string name;
double GPA;
int credits;
};
student::student() :
name("No name yet"), GPA(0.0), credits(0)
{
cout << "Default constructor entered!" << endl;
}
student::student(string s, double gpa, int nCredits) :
name(s), GPA(gpa), credits(nCredits)
{
cout << "Second constructor entered!" << endl;
}
void student::changeCredits()
{
cout << "Enter credits earned:" << endl;
cin >> credits;
cout << endl;
}
int student::getCredits()
{
return credits;
}
void student::changeGPA()
{
cout << "Enter GPA: " << endl;
cin >> GPA;
cout << endl;
}
double student::getGPA()
{
return GPA;
}
void student::displayStRec()
{
cout << " Name: " << name <<endl;
cout << " GPA: " << GPA <<endl;
cout << "Credits: " << credits <<endl;
}
student::~student()
{
cout << "Destructor entered!" << endl;
}
int main()
{
student s1, s2("John", 4.0, 42);
s2.changeCredits();
s2.getCredits();
s2.changeGPA();
s2.getGPA();
s2.displayStRec();
return 0;
}