p++ is faster because on compilation, it gets translated to three machine
instructions, where as p=p+1 needs four machine instructions. All machine
instructions take the same time.

For p++, the instructions are:

mov ax,

inc ax

mov,

ax

For p = p+ 1, the instructions would be,

mov ax,

mov bx, 1

add bx

mov,

ax

This is why p++ is faster than p+1