[Misiur]

Switch is your best friend

pawn Код:

#define strcpy(%0,%1) strcat(((%0)[0] = EOS, (%0)), %1)

forward CheckRank(playerid);
public CheckRank(playerid) {
    new 
        previousRank = pRank[playerid],
        rankmsg[82], 
        rankname[24];
        
    switch(pInfo[playerid][Kills]) {
        case 100..300: {
            pRank[playerid] = Master;
            strcpy(rankname, "Master");
        }
        case 301..500: {
            pRank[playerid] = Mastah;
            strcpy(rankname, "Mastah");
        }
        case 501..750: {
            pRank[playerid] = Promaster;
            strcpy(rankname, "Promaster");
        }
        default: {
            pRank[playerid] = Kid;
            strcpy(rankname, "Kid");
        }
    }
    if(pRank[playerid] != previousRank) {
        strcpy(rankmsg, "Hey, you've got promoted! Congratulations - you are now a ");
        strcat(rankmsg, rankname);
        SendClientMessage(playerid, -1, rankmsg);
    }
}

Remeber to declare all variables (Master/Mastah/Promaster/Kid)