Problem with constructor?

[KoshiB]

Ok. Im making a login program mostly as practice with various c++ things, and when i tried to compile the code, it gave me one error I can't figure out. I use MSV C++ 6 for my compiler. This is the error:

error C2512: 'Students' : no appropriate default constructor available

The error points to this line:

Students *stdnt = new Students[100];//Students not logged in

And here is the full source. It's large so be warned. I tried to comment it well to make it easy to read.

// Login Program made for MCC 
// For now DOS based
//
// Future features:
//
// 1)Saves data to textfile for backup purposes and
// informational purposes
//
// 2)Windows GUI
// 
// 3)Log time students logged in

// Programed by:
// Justin Allen
// 02/27/2006

#include <iostream>
#include <string>
#include <stdio.h>

using namespace std;

class Students
{
private:
	char firstName[26];
	char lastName[26];
	int idNum;

public:
	Students(char[26], char[26], int);
	void showData();
	void newStudent();
	void login();
	void logout();
	void setData(char[26], char[26], int = 0);
};

//Constructor
Students::Students(char firstname[26], char lastname[26], int idnum)
{
	firstName[26]=firstname[26];
	lastName[26]=lastname[26];
	idNum=idnum;
}

//Display data by admin
void Students::showData()
{
	cout << lastName << " , " << firstName;
}

//Sets data inside class
void Students::setData(char firstname[26], char lastname[26], int idnum)
{
	firstName[26]=firstname[26];
	lastName[26]=lastname[26];
	idNum=idnum;
}

//Main Function
int main()
{
	//Variable declaration
	int choice, count = 0, i;	
	int idnum, pwd;
	const int PWD = 01103657;//'secret' password
	char firstname[26];
	char lastname[26];
	
	//Pointer to new data structure in class
	Students *stdnt = new Students[100];//Students not logged in
	//Students *stdnt2 = new Students[100];//Student logged in

	do//Infinite(for now) Menu Loop
	{
		//Main Menu
		system("cls");//Clear screen
		cout << "**** MCC COMPUTER LAB LOGON ****\n";
		cout << "       !!!PLEASE LOGIN!!!       \n\n";
		cout << "Please choose:\n";
		cout << "1. Login\n";
		cout << "2. Logout\n";
		cout << "3. New Student\n";
		cout << "Pleas note that you are a New Student if\n"
			<< "this is your first time here this semester!!\n\n";

		cin >> choice;//Enters menu choice

		switch(choice)
		{
		case 1://Login student(not coded yet)
			//stdnt[].login();
			break;
		
		case 2://Logout student(not coded yet)
			//stdnt[].logout();
			break;
		
		case 3://Create new student
			cout << "Type 'exit' if you mistakenly entered new student prompt\n";
			cout << "Enter first name: ";
			cin >> firstname;
			if((stricmp(firstname, "exit") == 0))//checks for exit
			{
				break;
			}

			else//otherwise continues entering new student info
			{
				cout << "Enter last name: ";
				cin >> lastname;
				cout << "Enter ID number WITHOUT '@': ";
				cin >> idnum;
			}
			
			//Calls setData function
			stdnt[count].setData(firstname, lastname, idnum);
			count++;
			
			cout << "\n\n!!!Thanks for registering, please login now!!!";
			system("pause");
			break;

		case 8://Hidden admin display data function
			cout << "Enter password: ";
			cin >> pwd;
			if(pwd==PWD)//checks entered password 
			{
				cout << "Students not logged in:n";
				cout << "Last name, First name\n";
				if(count==0)
				{
					cout << "There are no student records yet";
				}

				else
				{
					for(i=0; i<count; i++)
					{
						stdnt[i].showData();//shows Data
					}
				}
				system("pause");
				break;
			}

			else
			{
				cout << "Wrong password!!";
				break;
			}
		
		default:
			//Error Handling
			cout << "\n\nError!! That option does not exist!!\n"
				<< "Please enter new choice!";
			system("pause");
			break;
		}

	}while(1);


	
	return 0;
}

Thanks in advance!

[SlyMaelstrom]

Your constructor expects arguements, but you haven't passed any. You'll need to either allocate the array of Students inside of your class or just make a default constructor.

Also, in your constructor, you can't assign arrays like this:

firstName[26]=firstname[26]

You need to use strcpy().

[7stud]

1) All objects of a class are created by a constructor.

2) When you define a constructor for your class, the compiler will not provide a default constructor.


Here:

Students *stdnt = new Students[100];

You are creating an array of 100 students and getting its location in memory. Each Student in the array must be created by a constructor. Since you cannot provide arguments to a constructor when you declare an array, the default constructor is called to create each Student in the array. Since you don't have a default constructor, you get an error.

When you get an error like this:

error C2512: 'Students' : no appropriate default constructor available

it's pretty obvious you need a default constructor--even if you don't know why. So, add a default constructor and have it display a message, e.g.

Student()
{ 
     cout<<"default constructor called"<<endl;
}

Then run your program again and look at the output to see when your default constructor is being called.