[CalvinC]

And then check if the player is connected.

Код:

if(!IsNumeric(inputtext) || strlen(inputtext) > 5) return SendClientMessage(playerid, -1, "{FF0000}You entered an invalid playerid.");
new id = strval(inputtext);
if(!IsPlayerConnected(id)) return SendClientMessage(playerid, -1, "{FF0000}You entered an invalid playerid.");