Thread: UDF

Which UDF are you referring to? http://en.wikipedia.org/wiki/UDF

User Defined Field? User Defined Function? Something else?

Well . . . are you asking how to create a function, and call it from within a loop?

Once you've created a function, you can call it from anywhere, nested for loops or otherwise. So perhaps you should read up on creating functions . . . .

Perhaps you have, say, a 2D array which you're iterating through, and you want to pass one element to a function, and you're not sure of the syntax?

[edit] If so, here it is:

Code:

void function(char c);  /* function prototype */

/* ... */

char data[WIDTH][HEIGHT];
int x, y;

for(x = 0; x < WIDTH; x ++) {
    for(y = 0; y < HEIGHT; y ++) {
        function(data[x][y]);
    }
}

/* ... */

void function(char c) {

}

[/edit]

There are a few things you have to keep in mind when creating a function:

Firstly, variables do not automatically appear inside a function from other functions (unless the variables are global -- but don't do that). You need to pass them in as parameters. Also, changes to variables made in the function are not typically reflected in the calling function. You need to pass pointers if you want the calling function to see changes made in the function.

You can also pass information back to the calling function by way of a return value -- but you only get one return value.

So, here's how you might do this. First, decide on the return type. I'll use void for now, indicating no return type.

Code:

void function(void) {

}

Now pass in the parameters. It's likely you'll need to pass in z.

Code:

void function(whatever z[N+1]) {

}

[If you want to pass in more variables, put a comma after the last variable, and include a type for each variable. For example,

Code:

void function(int one, int two, char three) {
}

]
Then you'll probably need to declare dx, dy, and dy as local variables inside this function.

BTW, if z has N elements, then z[j] is overflowing the array. If it has N+1 elements, you're safe.

Finally, I should note that your code is actually does absolutely nothing, except calculate dx, dy, and dz -- but that only once. Because the values of dz etc are overwritten in each loop, you don't need a loop at all if you don't want it.

There's a tutorial on this site about functions, but it's not too extensive. http://www.cprogramming.com/tutorial/c/lesson4.html

The best place to look is probably in a book (no pun intended). You might be able to find an extensive function tutorial online, but a book will probably go into greater depth.

Hint: if you're searching for information, don't search for "UDF" -- I'd never heard of it before. You'll probably find a lot more by looking for "functions" or "declaring functions in c" or something.

How are dx, dy, and dz "different"? The fact remains that you're doing an assignment over and over again in the loop, effectively overwriting the values of those variables, as far as I can see.

It's been a long time since I looked at a C book -- but you might try the Books Recommendations sticky. http://cboard.cprogramming.com/showthread.php?t=74079

Here's another tutorial (scroll down to "10. Functions"), but it uses bad practises such as implicit int and void main(). http://www.physics.drexel.edu/studen...eral/C_basics/
But at least it's quite complete.

Here's a less formal one: http://visualcplus.blogspot.com/2006...ions-in-c.html

Just keep searching, or buy a C book (I don't know which one, but don't pick something that says "in 24 hours" or "easy visual" or stuff like that . . . .)