Thread: Novice needs help with Functions

Hi guys,

First of all, I'm newto this board, so nice to meet you!

Well, now that introductions are over:

I'm a super fresh newbie to C++, and I'm having a hell of a time with fucntions. Basically, I'm trying to write an elementary program that passes variables into a function--the function then adds the variable and sends the results back into the prgram. Here is the code:

Code:

#include <iostream>

int myFunc(int x, int y);

int main()
{
	int a;
	int b;
	int c;

	std :: cout << "Enter a number \n";
	std :: cin >> a;
	std :: cout << "Enter another number \n";
	std :: cin >> b;
	myFunc();
	std:: cout << "myFunc is: " << c;
	return 0;

}
	
	int myFunc (a,b)
	{
		c = a + b;
		return c;
	}

For some reason, I get nothing but compiler errors when I try to run it. I've declared that the function will accept integers, and have listed that it will return integer values. I have no idea what I'm doing wrong. I know you guys have better things to do--and better problems to work on--but I really need some help. Any advice, or should I just hang my head in shame?

The line

Code:

  myFunc();

is just throwing away the returned value, since you don't assign it to anything. You need to assign it to the variable you print:

Code:

  c = myFunc();

Edit: Another error is that you should replace

Code:

  int myFunc (a,b)

with

Code:

  int myFunc (int a, int b)

you need to pass the variable you want the function to compute, and also the return value has to be passed as well...

so you need to put

Code:

 c = myFunc(a,b);

I know nothing about C++, but that's how you do it in C

What he said - my line was wrong (you need the "a, b" inside the parentheses).

have you ever heard of the...

Code:

using namespace std;

...function?

Teaching a newbie to use namespace std is a good way to avoid getting into prefixing.

It is better to declare exactly what objects you will be using.

Code:

#include <iostream>

using std::cout;
using std::endl;
using std::cin;

Is better and looks more effiecent than just putting namespace std. But all this is down to the individual programmer I guess, it is all down to personal taste.

Pass the variable to the function you need.

Code:

myFunc ( a, b );

Thank you, guys, for the advice. I think I am making headway. I re-read my entire text chapter on functions--for some reason, I am still confused by the concept of passing variables. However, I think I am making headway. I am able to compile now without errors, but the program won't run right--" Overloaded Function Error!" or something like that happens when I try to execute the program. Here is my revised version:

Code:

// Listing 5.4 - demonstrates variables
// scoped within a block

#include <iostream>

int myFunc(int a, int b);

int main()
{
	int a;
	int b;
	int c;

	std :: cout << "Enter a number \n";
	std :: cin >> a;
	std :: cout << "Enter another number \n";
	std :: cin >> b;
	c = myFunc(a, b);
	std:: cout << "myFunc is: " << c;
	return 0;

}
	
	int myFunc (int a,int b)
	{
		int c;
		c = myFunc(a,b);
		return c;
	}

I think I'll be able to figure it out, but I need to read ahead about overloading functions. Damn it! Everything was so easy before this. Damn these functions!

Has nothing to do with overloading - the 3rd-to-last line is supposed to be

Code:

  c=a+b;

not

Code:

  c = myFunc(a,b);

Or you could just put

Code:

return a + b

They would both achieve the same result

Success!!!

Thank-you for the help! It was such a silly mistake. I kept getting confused the concept of a function prototype, declaring the function, defining the function and calling the function. Essectially, I kept forgetting which one required me to use the exact name of the variables that I declared in main. Nevertheless, what was nebulous is now painfully clear. Here is my correction:

Code:

// Listing 5.4 - demonstrates variables
// scoped within a block

#include <iostream>

double myPay(double precd, double tpay);

using namespace std;

int main()
{
	//This program calculates the percentage of taxes
	// taken from a person' paycheck
	
	double precd;
	double tpay;
	double modu;

	cout << "Enter The Net amount of your check:\n";
	cin >> precd;
	cout << "Enter the gross amount earned on your check\n";
	cin >> tpay;

	modu= myPay(precd,tpay);

	
	cout << " You received" << modu << "% of your money!";

	return 0;
}

	double myPay(double precd, double tpay)
	{
	
		return precd / tpay;

	}

This is the same as the other one, with different variables and a different operator. For some reason I thought I had to declare the varibles inside the function--ignoring the obvious concept of "passing" the variables from main to the function.

I see you have taken some bad advice concerning namespaces. The way you originally used std:: was the best.

Usually newbies are advised to use "using namespace std;" if the teacher doesn't want to go into namespaces, because otherwise they would come with questions "How come 'cout' is undeclared?" This is just a lazy "fix" to get your program compiling, and hopefully proper usage of namespaces would be taught at a later time.

But if you already use std:: properly, starting to use "using namespace std;" is like going back to the stone age. This directive effectively says: I just need the program to compile somehow, and I don't care about the benefits of namespaces and I don't care if this language feature is even there.

Thanks for the tip. We were told to use std::, I was just trying something new. I'm going to read a bit more about namespaces, though, just for the hell of it. For some reason we haven't touched much on it yet.