question on recursive function

[dionys]

Hi guys

#include<stdio.h>


void p(int n){
   
   if(n > 0){
     p(n - 2); 
     printf("%d ", n); 
     p(n - 1);
    }
} 
int main(void) {
   p(4);
   
return 0;   
}

explain me plz: why does it print :2 1 4 1 3 2 1

Also can you explain me what is this statement:
int (*func())[20];

[quzah]

Walk through it on paper next time:

p(4)
    4>0 so...
    p(2)
        2>0 so...
        p(0)
            p(0), 0!>0 so it returns
        print 2
        p(1)
            1>0 so...
            p(-1), -1!>0 so it returns
            print 1
            p(0), 0!>0 so it returns
    print 4
    p(3)
    ...you do the rest...

As for:

int (*func())[20];

This is trying to be an array of 20 function pointers.

Quzah.

[dionys]

thanks a lot

another thing...
can you implement int (*fuct())[20]
in an example to understand what is going on(plz)?

[Prelude]

>This is trying to be an array of 20 function pointers.
No, it's a function returning a pointer to an array of 20 integers. An array of 20 pointers to function returning int would look like this:

int (*func[20])();

>can you implement int (*fuct())[20]
>in an example to understand what is going on(plz)?

#include <stdio.h>

int (*func())[20];

int
main(void)
{
  int (*array)[20] = func();
  int   i;

  for (i = 0; i < 20; i++) {
    printf("%d\n", (*array)[i]);
  }

  return 0;
}

int (*func())[20]
{
  static int a[20];
  int        i;

  for (i = 0; i < 20; i++) {
    a[i] = i;
  }

  return &a;
}

[pinko_liberal]

Is there anything wrong in the code to allocate arrays of a particular length below. I have never returned pointer to arrays before so I wanted to be sure.

#include <stdio.h>
#include <stdlib.h>

typedef int array_20[20];

array_20 *
func(void)
{
  array_20 *a;
  int i;

  a= malloc(sizeof *a);

  for(i=0;i < sizeof *a/sizeof (*a)[0];i++)
    {
        (*a)[i]=i;
    }

  return a;
}


int
main(void)
{
  array_20 *array;
  int   i;

  array=func();

  for (i = 0; i < 20; i++)
    {
        printf("%d\n", (*array)[i]);
    }

  free(array);
  return 0;
}

[Prelude]

>Is there anything wrong in the code to allocate arrays of a particular length below.
No, it's fine. You allocate the memory for an array of size 20 and have a pointer to an array point to that memory. Then later you free it. All is well, but it's easy to see why pointers to arrays aren't used much, look at that syntax.