Swap() func in the book Essential C does not compile

Question

wtf.c:11:6: error: expected declaration specifiers or '...' before '&' token Swap(&a, &b);

wtf.c:11:10: error: expected declaration specifiers or '...' before '&' token Swap(&a, &b);

Did not want to resort to StackOverflow for my personal problem but i cannot figure it out. The code is exactly the same as the book's. I've also tried making separated pointers and using them as arguments but i get the same error. Can someone shine some light on what am i doing wrong? I'm using gcc to compile the code.

static void Swap(int *x, int *y){
  int temp;
  temp = *x;
  *x = *y;
  *y = temp;
}

int a = 1;
int b = 2;

Swap(&a, &b);

I expected it to compile at least the exact example from the book but apparently not even that's possible.

nice file name. is this the exact code, without main function etc.? if you copy pasted the whole file, it might have been more helpful — Hayri Uğur Koltuk, Jan 10 '19 at 20:00
You need a `main` function, you can not call `Swap` in global scope. — David Ranieri, Jan 10 '19 at 20:01
Thank you guys and yes, this is the exact copy. The example is devoid of a main() function and it is not specified anywhere that i should be using it to call functions, at least not as far as i am in the book. — spaghettiBox, Jan 10 '19 at 20:17

bruno · Accepted Answer · 2019-01-10T20:10:55.477

2

#include <stdio.h>

static void Swap(int *x, int *y){
  int temp;
  temp = *x;
  *x = *y;
  *y = temp;
}

int main()
{
  int a = 1;
  int b = 2;

  Swap(&a, &b);
  printf("%d %d\n", a, b);
  return 0;
}

That compile and the execution print "2 1", as you can see swap works

You had the compiler errors because of the form Swap(&a, &b); which is not a declaration nor a definition (it is a function call)

As it is said in remark the entry point of any C program is the function main, automatically called, for more read documentation about C

edited Jan 10 '19 at 20:10

answered Jan 10 '19 at 20:05

bruno

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This has in fact worked. I wonder why this was not specified in the book... – spaghettiBox Jan 10 '19 at 20:14
@spaghettiBox: Usually, you see the function definition, followed by text that says something like *"You use this function thus:"*, and then the usage example. The idea is that the function definition is the code you add to your own program or library, and the use example shows how you *can* use it. It is not intended to be a self-contained example *program*. If you want a self-contained example program from such examples, you do exactly what bruno did here. So, you can think of this approach as shorthand; omitting the always-same "red tape". – Nominal Animal Jan 10 '19 at 21:02
Nominal Animal very well said, i'm simply used to being held by my hand and walked through the steps. I will look at this book differently henceforth. – spaghettiBox Jan 11 '19 at 04:40

Swap() func in the book Essential C does not compile

1 Answers1