10 replies to this topic

[mainevent403]

Hello,

I am new to these forums and new to c++ but not new to programming; however, I have run into an issue with an assignment from one of my classes.

I have a c++ project (made in visual studio 2010) with 3 sources files that I'm using:

// grade.h

// version 1

const int maxsize=20;

struct Student

{

	char stuID[5];

	int midterm;

	int final;

	int quiz1;

	int quiz2;

	double average;

	char grade;

};

class Stuclass

{

	public:

		//constructor

		Stuclass();

		// read data from a file

		void input();

		// output data to a file

		void output();

	private:

		Student myclass[maxsize];

		int numberofstudents;

		// calculate the average grade and final

		// letter grade for each student

		void calculation();

};

// grade.cpp : Defines the entry point for the console application.

//


#include "stdafx.h"

#include <iostream>

#include <fstream>

using namespace std;


void Stuclass::input()

{

	ifstream in_stream;

	in_stream.open("input.dat", ios::in);

	if(in_stream.fail())

	{

		cerr<<"Intput file opening failed.\n";

		cin.get();

		exit(1);

	}

	int x;

	// read number of students

	in_stream >> x;

	numberofstudents=x;

	for (int i=0; i<numberofstudents; i++)

	{

		// read Student ID (4-digit)

		in_stream >>myclass[i].stuID;

		// read Quiz1

		in_stream >>myclass[i].quiz1;

		// read Quiz2

		in_stream >>myclass[i].quiz2;

		// read Midterm

		in_stream >>myclass[i].midterm;

		// read Final

		in_stream >>myclass[i].final;


		// calculate the average

		myclass[i].average = (.25 * (myclass[i].quiz1 + myclass[i].quiz2)) + 

			(.25 * (myclass[i].midterm)) + 

				(.50 * (myclass[i].final));

	

		// calculate the letter grade

		if(myclass[i].average >= 90)

		{

			myclass[i].grade = 'A';

		}

		if(myclass[i].average >= 80 && myclass[i].average < 90)

		{

			myclass[i].grade = 'B';

		}

		if(myclass[i].average >= 70 && myclass[i].average < 80)

		{

			myclass[i].grade = 'C';

		}

		if(myclass[i].average >= 60 && myclass[i].average < 70)

		{

			myclass[i].grade = 'D';

		}

		if(myclass[i].average < 60)

		{

			myclass[i].grade = 'F';

		}

		

	}

	in_stream.close();

}


void Stuclass::output()

{

	ofstream out_stream("output.dat");

	if(out_stream.fail())

	{

		cout<<"Output file opening failed.\n";

		exit(1);

	}

	out_stream << "StuID\tQuiz1\tQuiz2\tMidterm\tFinal\tAverage\tFinal Grade\n";

	for(int i = 0; i< numberofstudents; i++)

	{

		out_stream << myclass[i].stuID << "\t" <<

		myclass[i].quiz1 << "\t" <<

		myclass[i].quiz2 << "\t" <<

		myclass[i].midterm << "\t" <<

		myclass[i].final << "\t" <<

		myclass[i].average << "\t" <<

		myclass[i].grade << endl;

	}

	out_stream.close();

}


void Stuclass::calculation()

{

}

#include "stdafx.h"

#include <iostream>

using namespace std;


//int _tmain(int argc, _TCHAR* argv[])

int main()

{

	Stuclass classroom();

	cin.get();

	classroom.input;

	classroom.output;

	return 0;

}

When building the source, I get 2 errors in int_tmain at classroom.input; and classroom.output; The errors both say "error C2228: left of '.input' must have class/struct/union." What I don't get is this: classroom is an Instance of my Stuclass class, so why would I get an error like this? If anyone could help me, or at least give me hints to help me learn why this happens, I would be very thankful. If possibly, provide an explanation so I know what I'm doing wrong. Thank you

[Skippy]

I don't know if this is the issue, but you need to make sure you include parameter syntax to a function call, even if you don't pass any parameters.

i.e.

classroom.input();

//not 

classroom.input;

Although it doesn't make sense that classroom.input would return an error. Because classroom.input should return the address of the input() function.

[mainevent403]

Yeah, i had originally tried it that way but it unfortunately yielded the same errors for me when building, thanks for the quick reply though.

[Flying Dutchman]

classrom.input;

classrom.input();

These are not the same in C++ (I'm pretty sure they can't even exist at the same time). First line is an attribute (variable) and second is method (class function).

Comment on the code:

int x;

// read number of students

in_stream >> x;

numberofstudents = x;

Why not like this?

in_stream >> numberofstudents;

[mainevent403]

I suppose it would make sense to do it that way, but it still doesn't solve the main problem I'm having where I can't compile, thanks for the optimization tip though :].

[Flying Dutchman]

What error do you get?

[ZekeDragon]

Your problem is the compiler is parsing this:

Stuclass classroom();

to be a forward function declaration, not a class instance. Do this instead:

Stuclass classroom;

That should fix it.

[Flying Dutchman]

ZekeDragon said:

Your problem is the compiler is parsing this:

Stuclass classroom();

to be a forward function declaration, not a class instance. Do this instead:

Stuclass classroom;

That should fix it.

Actually, those are the same; you can create instances either way with ctor that takes no parameters.

[mainevent403]

That seems to be the problem, thank you very much :]

[Xupicor]

@Flying Dutchman: actually, ZekeDragon is right. TIAS.

#include <iostream>


struct Foo {

    int x;

    

    Foo() {

        std::cout << "Foo!\n";

    }

};


int main() {

    Foo foo(); // thinks it's forward declaration, should be Foo foo;


//    foo.x = 0; // whoops:

// cpp:14:9: error: request for member 'x' in 'foo', which is of non-class type 'Foo()'

    

    return 0;

}

This code will not print "Foo!" as you might expect. ;)

[Flying Dutchman]

My bad, I assumed it works because I never had problems with this. Or maybe I mixed it with something... Anyways, thanks for pointing it out, learned something new. :)