[Scaleta]

'!' - If the outcome of the conditional statement is true, then it will be false and vice-versa.

Kind of a bad explanation...

pawn Код:

new one; // one is 0
if(!one) { 
    // this will go through
}

one = 1;
if(!one) {
    // this will not go through
}

If we did on‌e = 1, then the if statement would be considered false and move on.

Edit: found a better explanation.

https://wiki.alliedmods.net/Pawn_tutorial#If_Statements (nothing to do with SA-MP, still good resource)