Novice needs help with Functions

This is a discussion on Novice needs help with Functions within the C++ Programming forums, part of the General Programming Boards category; Hi guys, First of all, I'm newto this board, so nice to meet you! Well, now that introductions are over: ...

  1. #1
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    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?

  2. #2
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    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)

  3. #3
    The C eater *munch*
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    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

  4. #4
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    What he said - my line was wrong (you need the "a, b" inside the parentheses).

  5. #5
    Sanity is for the weak! beene's Avatar
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    have you ever heard of the...
    Code:
    using namespace std;
    ...function?

  6. #6
    Its hard... But im here swgh's Avatar
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    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 );

  7. #7
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    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!

  8. #8
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    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);

  9. #9
    Its hard... But im here swgh's Avatar
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    Or you could just put

    Code:
    return a + b
    They would both achieve the same result

  10. #10
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    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.

  11. #11
    The larch
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    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.

  12. #12
    Cat
    Cat is offline
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    Quote Originally Posted by anon
    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.
    I agree. "using namespace std;" is something that should be avoided in any good program. I don't even like individual using statements -- I like to see each place where I use something in the std:: namespace because my programs generally have functions and classes in three, four, five namespaces. It makes it MUCH more clear to prefix everything like your original code.

    There are a few good uses of "using" (and a few times you can't accomplish something without it) but they're special/unusual cases. You shouldn't use it just to get rid of std:: in your code (which make the code more readable).
    You ever try a pink golf ball, Wally? Why, the wind shear on a pink ball alone can take the head clean off a 90 pound midget at 300 yards.

  13. #13
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    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.

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