what difference between while(*p){p++;} ,while (*++p){;} and while(*p++){;}?

Question

It\'s about strcat function.

while (*p)
    p++;

and

while (*++p)
    ;

both works, but

Answer 1

Let's assume that p is a string.

while (*p) p++; /* (1) */
while (*++p) ;  /* (2) */
while (*p++) ;  /* (3) */

• (1) is different from (2) if p is an empty string.
• (1) is different from (3) because with (3), even if the current value of *p is a '\0' character, p is incremented.