[Matnix]

For me this way is better, I prefer this one and it's an example (untested for the moment) hope you like this way.

pawn Код:

// On Player Text

new string[256], Name[MAX_PLAYER_NAME];
GetPlayerName(playerid, Name, sizeof (Name));

IsPlayerAdmin(playerid); 
{
    format(string,sizeof(string), "[ADMIN] %s said : %s", Name, text);
    SendClientMessageToAll(-1, string);
    return 0;
}
// etc your others code