for an array a , is a same as &a

[agarwaga]

#include <stdio.h>
void display(int* arr,int len){
    int i;
    for(i = 0; i < len; ++i){
	printf("%d ",arr[i]);
	printf("\n");
    }
}
main()
{
    int arr[] = {1,2,3};
    printf("%d  %d\n",arr,&arr);
}

are the two arr and &arr same ? , can they be used interchangeably ?
if not what is the difference ?
gcc gives this warning:

test23.c: In function `main':
test23.c:13: warning: passing arg 1 of `display' from incompatible pointer type

[agarwaga]

#include <stdio.h>
void display(int* arr,int len){
    int i;
    for(i = 0; i < len; ++i){
	printf("%d ",arr[i]);
	printf("\n");
    }
}
main()
{
    int arr[] = {1,2,3};
    printf("%d  %d\n",arr,&arr);
    display(&arr,3);
    display(arr,3);
}

This is the code i am referring to

[Prelude]

>are the two arr and &arr same ? , can they be used interchangeably ?
No, and no. The fact that your compiler warns you about it should be a hint that they're not compatible types.

>if not what is the difference ?
A level of indirection. For the following array:

int a[10];

a is almost always treated as the address of the first element (&a[0]), but &a is treated as the address of the array as a whole. The address may be the same, but the types are different. a is a pointer to int and &a is a pointer to an array of ten int.

To use both, you need two different functions:

#include <stdio.h>
void display1(int* arr,int len){
  int i;
  printf("display1: ");
  for(i = 0; i < len; ++i)
    printf("%d ",arr[i]);
  printf("\n");
}
void display2(int (*arr)[3],int len){
  int i;
  printf("display2: ");
  for(i = 0; i < len; ++i)
    printf("%d ",(*arr)[i]);
  printf("\n");
}
int main(void)
{
  int arr[] = {1,2,3};
  printf("%d  %d\n",arr,&arr);
  display2(&arr,3);
  display1(arr,3);
  return 0;
}

[Salem]

> are the two arr and &arr same ?
They're the same by value, but the types are different.
Compare a pointer to a struct and a pointer to the first element of a struct - same value, different type.

> can they be used interchangeably ?
No.

> if not what is the difference ?
arr is a pointer to the first element of the array (like &arr[0] is), and &arr is a pointer to the whole array.

void display(int (*arr)[3],int len);
Would be the prototype of the function for passing a pointer to the whole array.

[Salem]

Spooky

[agarwaga]

thanks a lot