Learning C

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Is there a drawback to it though?

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Yes - a lot, and only few reasons to use it, that do not appear till the real advanced programming technics. So for now - just avoid using goto always.

You forgot to check that the user input is bigger than 0 - you printing z anyways

You can use break to exit loop on condition in the middle

there is also

while (1) {

the infinite loop, ie., it never ends, but while (x>0) is probably truer to your intentions...

Why is it "illegal" to use main() like that, and (if so) where are the kompiler kops?

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Originally Posted by MK27

Why is it "illegal" to use main() like that

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As far as I can tell, it is legal to call main() in a C program, though it is bad practice. It is the C++ standard that forbids the use of main() within a program.

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Originally Posted by vart

Yes - a lot, and only few reasons to use it, that do not appear till the real advanced programming technics. So for now - just avoid using goto always.

You forgot to check that the user input is bigger than 0 - you printing z anyways

You can use break to exit loop on condition in the middle

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Ok, will do. Is there any particular reason? Is it resource consuming or something?

It doesn't seem to be an oversight either.

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5.1.2.2.3 Program termination
1 If the return type of the main function is a type compatible with int, a return from the
initial call to the main function is equivalent to calling the exit function with the value
returned by the main function as its argument; [...]

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No, goto isn't that resource consuming at all. It's considered a bad idea because it's very unstructured. One of the powers of C is that you can organize your code and your data into structures and functions. When you use goto, it totally disregards that structure, and so it's very easy to run into bugs and problems when your code gets more complex.

A better option is to control flow with a loop and the tools that come with a loop (in this case - the break statement), or maybe even a recursive function (depending on what you're trying to do). Really, there's nothing INHERENTLY EVIL about using goto, it's just that if you have to use goto, your programming probably isn't organized very well.

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Originally Posted by Alexander

Ok, will do. Is there any particular reason? Is it resource consuming or something?

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No, it just jumps to a different part of the code.
The problem with using goto is that it's Addictive, Lazy, Unneccessary, and makes your code hard to read if it becomes littered with goto statements.
I think I've only had a valid reason to use goto once or twice in my career. Unfortunately I was using Java which didn't let me use it, so I had to use a messier option.
So until you've had several years experience in programming, just pretend goto doesn't exist. I probably should have been more explicit with my sarcasm. ;)

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Originally Posted by cpjust

No, it just jumps to a different part of the code.
The problem with using goto is that it's Addictive, Lazy, Unneccessary, and makes your code hard to read if it becomes littered with goto statements.
I think I've only had a valid reason to use goto once or twice in my career. Unfortunately I was using Java which didn't let me use it, so I had to use a messier option.
So until you've had several years experience in programming, just pretend goto doesn't exist. I probably should have been more explicit with my sarcasm. ;)

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xD So it's pretty much just ugly coding? Well, I'll try and pretend it doesn't exist then. I don't think I'll need to use it quite yet any ways. Thanks.

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Originally Posted by Alexander

xD So it's pretty much just ugly coding? Well, I'll try and pretend it doesn't exist then. I don't think I'll need to use it quite yet any ways. Thanks.

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There is no code in C that actually REQUIRES the use of goto. There are some cases, when the code is quite complex, where a goto makes the code simpler - typically, the case is where you have a lot of "creation steps", and if one step or another fails, you have to clean up some of the stuff you've created so far - you either end up with a hairy mess of lots of nested if-statements and/or repeated cleanup code, or you use a goto to jump to one piece of cleanup code. C++ can be a bit better on this because of automatic destruction of objects when they go out of scope (e.g. at end of a function).

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Mats

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Originally Posted by Alexander

Oh! Now I get what you mean!

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#include <stdio.h>

int main(void){

        int x, z = 0; //variables

        while(x>0){ //check user input
                scanf("&#37;d",&x); //user input
                int y;
                for(y=1;y<=x;y++){ //loop to add all integers between 0 and x together
                        z += y;
                }

                printf("%d\n",z); //print result
        }

        return 0; //end
}

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I don't think your while loop will work. Look at what is happening.

Variable x is initialized
Variable z is initialized
While (x > 0) ----- x is nothing, skip loop
End program

Also, I think you may have misunderstood your teachers instructions (unless his assignment is just terribly written). The way I understand it, he wants each number between 0 and x to be printed to the screen. So if the user enters 4, he wants 1, 2, and 3 printed. If the user enters 4 in your program, as it is now, it will print 10.

Here is an example:

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int main() {
        int x = 0;
        int z = 0;

        for(;;) {
                scanf("%d", &x);
                if (x <= 0)
                        break; //Exit for loop

                int y = 0;

                // In case your teacher is anal, 0 and x will not be printed
                // " ... prints the numbers [BETWEEN] 0 and the entered number."

                for (y = 1; y < x; y++)
                        printf("%d\n", y);
        }

        return TRUE;
}

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Oh jeez, yeah, you're right. I got myself confused. xD I thought he meant to find the sum of all the numbers between 0 and the entered number because that's what he did last chapter. ^^;

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Originally Posted by matsp

There is no code in C that actually REQUIRES the use of goto. There are some cases, when the code is quite complex, where a goto makes the code simpler - typically, the case is where you have a lot of "creation steps", and if one step or another fails, you have to clean up some of the stuff you've created so far - you either end up with a hairy mess of lots of nested if-statements and/or repeated cleanup code, or you use a goto to jump to one piece of cleanup code. C++ can be a bit better on this because of automatic destruction of objects when they go out of scope (e.g. at end of a function).

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Mats

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Ah ok, so it's really more of a last resort?

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Originally Posted by Alexander

Ah ok, so it's really more of a last resort?

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You'll never need to resort to it.

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Originally Posted by Alexander

Ah ok, so it's really more of a last resort?

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Originally Posted by kpreston

You'll never need to resort to it.

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There's always a way to write code in a way so that you don't need to use goto; it's just that in extremely rare circumstances it can simplify code.
If you use goto more than once a year, you're over-using it.

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Originally Posted by cpjust

There's always a way to write code in a way so that you don't need to use goto; it's just that in extremely rare circumstances it can simplify code.
If you use goto more than once a year, you're over-using it.

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Unless your job is to write device drivers, I would say. In a code-review on some code that I had modified, someone pointed to a initialization function that has 12 goto's (all to the same label, all when somethng couldn't be initialized). It wasn't my doing, but I couldn't really find a better solution after it was pointed out (aside from splitting the function into many small functions and using many if/else branches - which would just make the function more complicated).

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Mats