Answer 1

here X++ means X=X+1

Answer 2

Answering your'e own question. Great. Wrong spelling.

Answer 3

There are two possible spellings:

1. X++
2. ++X

Both will add 1 to the value of X and the new value overrides the old one.

BUT there is a significant difference of use.
In the first case the return value of the statement will be the value of X BEFORE the increase.
While in the second case the return value of the statement will be the value of X AFTER the increase.

eq:
int X = 3;
// following if condition will NOT evaluate to true, because first the value of X will be compared and after that X will be increased
if (X++ == 4) { ... }

int X = 3;
// following if condition WILL evaluate to true, because first of all the value of X will be increased and afterwards the new value of X will be compared
if (++X == 4) { ... }