The compiler doesn't pass any size information when you pass an array into a function. The function just gets a pointer. If you take the sizeof the array, you'll get the size of a pointer on your system:

[eric@rangely foo]$ cat foo.c

    #include <stdio.h>

    int test (int arr[10])
    {
        printf ("%lu\n", sizeof (arr));
        return 0;
    }

    int main (int argc, char *argv[])
    {
        int arr[5];
        test (arr);
        return 0;
    }

[eric@rangely foo]$ gcc foo.c -Wall -o foo && ./foo

8

(EDIT: fixed formatting)