Justification

Pointer subtraction only has meaning for determining an offset.

Note

The unqualified type of a pointer is its type without "const", "volatile", etc.

Example

char *p;
char *q;
float *f;

static const char message[] = "This is a message for ...";
float g = 0.0;

p = &message[5];
q = &message[10];
f = &g;

printf("Number of elements: %d\n", q - p); /* RIGHT */
printf("Number of elements: %d\n", q - f); /* WRONG */