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:

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#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:

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  myFunc();

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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();

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Edit: Another error is that you should replace

Code:

---

  int myFunc (a,b)

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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:

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using namespace std;

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...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:

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  c=a+b;

---

not

Code:

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  c = myFunc(a,b);

---

Or you could just put

Code:

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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:

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// 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.

Quote:

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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.

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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).

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.