[Shinja]

Affan's code is wrong..
Try this

PHP код:

new pLastMsg[100][MAX_PLAYERS];
public OnGameModeInit()
{
    for(new i, j=MAX_PLAYERS; i<j; i++) { format(pLastMsg[i], 100, "!9sd4f"); }
    return 1;
}
public OnPlayerText(playerid, text[])
{
    if(!strcmp(text, pLastMsg[playerid], true))
    {
        //Have wrote the same message
        //Do something
        //return 0; to prevent sending the message
    }
     format(pLastMsg[playerid], 100, text);
    return 1;
}