How can the compiler in C get the difference between the address of the first element of the array and the address of the whole array?

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Given this problem and I'm fully aware of the facts of :

1) The name of an array is a fixed pointer to the first element of it.

2) The name of a 2D matrix is the address of the first 1D array of it.

3) and the difference between x[i] and &x[i] in arithmetic operations (where i is a non negative integer).

The compiler is MinGW How can the compiler in C get the difference between the address of the first element of the array and the address of the whole array although they hold the same numeric value ? 

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
int main(void)
{
    int x[3][3] = {1,2,3,4,5,6,7,8,9} ; 
    int *p  ; 
    for(p = &x[0] ; p < &x[0] + 1 ; p++) //Warning: comparison of distinct pointer types in this line of code 
        printf("%d\n",*p) ; 

    return 0 ; 
}
mingw compiler-construction c
1 Answers

You're assigning / comparing two different pointer types.

x has type int [3][3], i.e. an array of size 3 of an array of size 3 of int. From there, x[0] has type int [3], i.e. array of size 3 of int.

Subsequently, &x[0] has type int (*)[3], i.e. a pointer to an array of size 3 of int. In contrast, p has type int *, i.e. pointer to int. These are distinct types, which is why the compiler is giving you a warning.

The compiler parses expressions in more-or-less the manner I described, looking at the type of an object and seeing how the type of the resulting expression changes as each operator is applied.

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