Not Declared In Scope

[Kroggor]

Can anyone please help? I really don't understand what's wrong with my program. Whenever I try to compile it, I end up with the phrase:
prog.cpp: In function ‘int main()’:
prog.cpp:30:18: error: ‘year’ was not declared in this scope
isfourdigit(year);

#include <iostream>
#include <cstdlib>
using namespace std;

bool isfourdigit(short int year);
bool isleapyear (short int year);
char userInput;
short int yearNumber = 0;

int main()
{
    do
    {
    	system("cls");

		cout << "Test if a Year is a Leap Year" << endl;
		cout << "-----------------------------" << endl << endl;
		cout << "Enter a 4-digit year: ";
		cin >> yearNumber;
    	cout << endl << endl;
    	
    	isfourdigit(year);
    	isleapyear(year);
    	
    	if (isfourdigit(year) == 1)
    	{
    		cout << "Error: Enter a 4-digit year!";
		}
    	else
    	{
    		if (isleapyear(year) == 1)
    		{
    			cout << "Year " << yearNumber << " is an ordinary year.";
    		}
    		else
    		{
    			cout << "Year " << yearNumber << " is a leap year.";
    		}
		}
    	
    	cout << endl << endl;
    	cout << "Run the program again?[y/n]: ";
    	cin >> userInput;

    	return 0;	
    } while (userInput == 'y' || userInput == 'Y');
}

bool isfourdigit(short int year)
{
	if (yearNumber < 1000 || yearNumber > 9999)
	{
		year = 1;
	}
	else 
	{
		year = 0;
	}
	
	return year;
}

bool isleapyear(short int year)
{
	if (yearNumber % 4 == 0)
	{
		if (yearNumber % 100 == 0)
		{
			if (yearNumber % 400 == 0)
			{
				year = 1;
			}
			else
			{
				year = 0;
			}
		}
		else
		{
			year = 1;
		}
	}
	else
	{
		year = 0;
	}
	
	return year;
}

[Zhuge]

Please use code tags.
http://www.cplusplus.com/articles/z13hAqkS/

Where is the variable 'year' declared?

[Kroggor]

Whoops, I'll fix that. Also, doesn't it count that I declare the "year" variable in the bool functions? Sorry, I'm still a beginner and don't understand much. XD

[Zhuge]

On line 23, for example, you try to pass the variable 'year' as a parameter to your function, but there isn't any such variable defined in main(). What value/variable where you trying to pass to it?

[Kroggor]

Basically, I wanted int main() to perform the bool functions so that "year" can be assigned the value of 1 or 0.

For example, in line 22, I declared the function so that it would have to skip to line 49 and calculate whether "year" is 1 or 0. After that, the bool isfourdigit function will return the data to int main so that it can do the next procedures.

I'm just not sure if I declared the functions in int main correctly, if the data was really returned, or if my logic is correct.

Did that help?

[long double main]

The year in your isfourdigit and isleapyear functions have nothing to do with each other, or with the (non-existent) year in main.

Perhaps a quick recap on functions is in order:
http://www.cplusplus.com/doc/tutorial/functions/

What I would do is move

char userInput;
short int yearNumber = 0;

into main() (global variables are typically frowned upon), and change your functions to

bool isfourdigit(short int yearNumber)
{
    if (yearNumber < 1000 || yearNumber > 9999)
    {
        return false; // You originally had 'year = 1;' here (presumably corresponding to 'true'),
                      // but I felt that returning false was more appropriate since the function
                      // is called 'isfourdigit' and if we're in this branch of the if statement,
                      // then the number is NOT four digits.
    }
    else 
    {
        return true;
    }
}

bool isleapyear(short int yearNumber)
{
    // Similar to above 

(Basically, make yearNumber your parameter and return true or false instead of setting a year variable).

Your function calls in main would then simply be

if (!isfourdigit(yearNumber)) // if NOT four digits -- 
{                             // makes more sense than "if 'is four digits' is 1 ( == true?)"
    cout << "Error: Enter a 4-digit year!";
}
else
{
    if (!isleapyear(yearNumber))
    {
        cout << "Year " << yearNumber << " is an ordinary year.";
    }
    else
    {
        cout << "Year " << yearNumber << " is a leap year.";
    }
}

[Kroggor]

Oh wow, it actually works. Thanks, you guys are awesome. :)