[C] Pointer to an array

--------------- output from my console ------------
$ cat code1.c
#include <string.h>
int main()
{
   char usr_data[128];
   memset( &usr_data, 0, 128 );
   return 0;
}

$ gcc code1.c
$ md5sum a.out
653c4838fdbbdde05c832f79765fa143  a.out
$ nano code1.c
$ cat code1.c
#include <string.h>
int main()
{
   char usr_data[128];
   memset( usr_data, 0, 128 );
   return 0;
}

$ gcc code1.c
$ md5sum a.out
653c4838fdbbdde05c832f79765fa143  a.out
--------------- output from my console ------------

There a few things I would like you to note.
1. The parameter for the memset is first "&usr_data", then it is
"usr_data"
2. The md5sum for the generated binary file is identical. Also the 
behaviour as far as I could tell is identical. Also sha1sum is 
identical. So it looks like the binary files are identical.

Question: How is it possible that the binary files are identical with 
these two different source codes?

And how is it possible that both applications fill the usr_data with 
zeroes? Shouldn't the first example just cause somekind of error? I 
would understand if the behaviour in that case would be undefined and is 
just happens to work correctly, but because the binary files are 
identical, it doesn't make sence.


TIA