new to "C" return question

ok first thanks for helping.

I'm new to programming in general and I decided I'd start with C. I found a pretty sweet tutorial and I'm plugging along but I have a question.

I see in the tutorial that at the end of an "if" block the tutorial has the command "return 0;"

I have written a program below just to kind of get my feet wet and I omitted the "return" line intentionally. It compiles and runs just fine so my question is what does the return line do, do I really need it and how do I use it and it's output later on for better coding?

Thanks again


#include <stdio.h>

int x, y, z;

main()
{

/*get some data here*/
printf("\nEnter a number: ");
scanf("%d", &x);


printf("\n Now enter another number: ");
scanf("%d", &y);
printf("\nYou entered %d, and %d\n", x, y);

/*test values here*/
if (x == y)
printf("%d is equal to %d\n",x,y);
else if (x > y)
printf("%d is greater than %d\n",x,y);
else
printf("%d is less than %d\n",x,y);
}

If you look a little bit down the page, you'd see this thread about return.

You've also gotten yourself into some bad habits.
You want to get rid of the implicit main.
And also use code tags around code you post. Like:
[code]int x, y, z; /* Etc */[/code]

I'll do that with the code from now on. I haven't been on a board of any kind in ages so my board etiquette probably could use some work as well.

implicit main, if I read your link properly basically it said that you need to define what type of data your function carries? is that correct or am I not understanding things.

what should I have done in the code above? I want to learn and develop "good" coding habits and I want to move onto C++ and Objective C after I have some skills in C so I really appreciate the feedback

It means you must select the return type for the function. And for main it's really easy, because it always returns int.
Also, if you're looking to use C++, I would suggest that you really start with C++ right away instead of going C and then C++. The reason is that many things that are good in C are taboo in C++. C++ has an entirely different way of thinking too.

In the code above, you should use int main, the global variables should really be local variables and the "z" variable could be deleted since it isn't used.

yeah but I'm going to use that z variable later when I expand on the code and start using logical operators. to try and do cooler stuff

I know this is a little off topic but I read your void main() link in your signature and I'm a little lost by all of it, I also read your scanf link also and I know that's way above my head,

just as a good practice should you always have your main function be on type int? should you use int type for your functions most of the time?

If you want the short story, just use int main() or int main(void) and always return an integer from main().

http://faq.cprogramming.com/cgi-bin/...&id=1043284376

Quote:

---

Originally Posted by demuro1

just as a good practice should you always have your main function be on type int? should you use int type for your functions most of the time?

---

Main should always return int. So says the standard, so that's all there is to it.
For your own functions, what you return is up to you (each function is usually different). If you don't need to return anything, you can use void.

Quote:

---

Originally Posted by Elysia

Main should always return int. So says the standard, so that's all there is to it.

---

No it doesn't. It says the implementation is free to do others.

Quote:

---

Originally Posted by &#167; 5.1.2.2.1.1 of the C99 standard / homepages.tesco.net/J.deBoynePollard/FGA/legality-of-void-main.html

It shall be defined

• with a return type of int and
  
  • with no parameters [...] or
  • with two parameters [...] or equivalent;
  or
• in some other implementation-defined manner.

---

Oh? I feel a possible clash of the standards.
Microsoft clearly referred to "void main" as a Microsoft extension.

EDIT:
Ah yes, even though it might "allow" non-int main, it clearly specified that what is returned to the OS then is undefined:

Quote:

---

Originally Posted by &#167; 5.1.2.2.3.1, C Standard

If the return type is not compatible with int, the termination status returned to the host environment is unspecified.

---

To make matters worse, void main is disallowed in C++:
http://homepages.tesco.net/J.deBoyne...void-main.html
But unfortunately legal in C. Something they really should change.

It very well maybe in C++ (since C++ does not provide this "loophole").

What does "returning int" mean? In my program the name of main was "int main(void)" (just because I had been told to put that). But I didn't use any integers in my main, let alone "return" them (I don't know what returning means anyway =/). I just used floats. Nothing seems to be wrong with the program when I run it, but is there something I should know about "returning int"?

Thanks for the help,

Jake

When you return something, it is more like "response by return" in mail correspondence than returning books to a library or some such.

In the case of int main() you tell the compiler "my main function will return an integer value". Convention is that you return 0 (or EXIT_SUCCESS - which is zero) as the return value from a "successful" application.

--
Mats

When you type "return 0;", you are returning an int. 0 is a number that has type int, and the return returns it from the function.

Returning a value from a function means that the caller will be able to use the function as part of an expression.

Code:

---

int get_42(void)
{
    return 42;
}

int get_10(void)
{
    return 10;
}

int main()
{
    int sum_of_two_nums;

    sum_of_two_nums = get_42() + get_10();

    printf ( "The sum of 42 and 10 is: %d\n" , sum_of_two_nums ) ;

    return 0 ; /* Returning 0 from main() means the program has ended successfully */
}

---

ok so I have another question now on returning numbers.

I have gotten this little program to run as I'd like it to but now I'm trying to do more with the code. basically I'm trying to make everything run as a function so all I do is call functions.

originally input() was part of main(). not only that but the printf() lines at the end of mult() and div() were incorporated in main() as well. Everything was fine until I tried to take the content that is in input() out of main(). the first section of code works perfectly. the second section is what I'm trying to make work in the same way. Can someone explain to me where my mistake is?

Thanks a million

Code:

---

/*
        Learning the ropes
        This Works!!!!
 */

#include <stdio.h>

int x,y;
float z,r;

int mult(int x,int y);
float div(int x,int y);


int main()
{
        printf("\nPlease enter a number: ");
        scanf("%d",&x);
        printf("\nPlease enter a second number: ");
        scanf("%d",&y);
       
       
        mult(x,y);
       
        printf("\nand");
       
        div(x,y);
       
        printf("\nHave a nice Day!!!\n");
               
        return 0;
}


int mult(int x,int y)
{
        z=x*y;
       
        printf("\n%d times %d equals %.2f",x,y,z);
       
        return 0;
}


float div(int x,int y)
{
        z=x/y;
        r=x%y;
        r=r/y;
        z=z+r;
       
        printf("\n%d divided by %d equals %.2f",x,y,z);
       
        return 0;
}

---

Code:

---


/*
        Learning the ropes
        got it to work now trying to add functions instead of just
 */

#include <stdio.h>

int x,y;
float z,r;

int mult(int x,int y);
float div(int x,int y);
float input(int x, int y);


int main()
{
        input(x,y);
       
        mult(x,y);
       
        printf("\nand");
       
        div(x,y);
       
       
        printf("\nHave a nice Day!!!\n");
       
       
       
       
       
        return 0;
}


float input(int x, int y)
{
        printf("\nPlease enter a number: ");
        scanf("%d",&x);
        printf("\nPlease enter a second number: ");
        scanf("%d",&y);
       
        return x,y;
}
       


int mult(int x,int y)
{
        z=x*y;
       
        printf("\n%d times %d equals %.2f",x,y,z);
       
        return 0;
}

float div(int x,int y)
{
        z=x/y;
        r=x%y;
        r=r/y;
        z=z+r;
       
        printf("\n%d divided by %d equals %.2f",x,y,z);
       
        return 0;
}

---

You can return x, or you can return y, but not both (and certainly not as a float). Also note that just because the letters are the same does not mean that x and y in input have any relation to x and y in main.

You can't return multiple values that way from a function. Instead, you need to pass a pointer to the variables:

Code:

---

#include <stdio.h>

// Receive pointers to the variables
void input(int *x, float *y)
{
  printf("Enter an integer: ");
  scanf("%d", x);
  printf("Enter a real number: ");
  scanf("%f", y);
}

int main(void)
{
  int x = 0;
  float y = 0.0f;

  // Pass the addresses of the variables
  // to the function.
  input(&x, &y);

  // Print the values of the variables
  printf("Got %d and %f\n", x, y);
  return 0;
}

---

I've heard of pointers but haven't learned about them yet. If I understand your code though the main difference seems to be the asterisk in front of x and y when you "declare" (is that even what it's called) them in input(). also you set initial values in main() and when you call the function you use & instead of the variable type. am I missing any key data about these and are my assumption correct?


thanks for the help by the way?

edit:

also you just wrote the function. would the prototype look like this

Code:

---

void input(int *x, int *y);

---

or like this

Code:

---

void input(int x, int y);

---

Yes, pointers mean you put a * before the type, between the type or beside the name:
int* x
int * x
int *x
All the same thing.
And since pointers hold the address of something, you do indeed need to pass the variables using &, to pass their address.

Perhaps it would be best to study pointers a little before you start using them.