Read everything with it's meaning.
pawn Code:
new gVar_Rank[MAX_PLAYERS]; //This is the variable where all the player's rank is stored.
public OnPlayerDeath(playerid, killerid, reason) //What all things happen when a player dies?
{
gVar_Rank[killerid]++; //The Rank of killer goes up++
gVar_Rank[playerid]--; //The Rank of the person died gets low--
if(gVar_Rank[killerid] < 10) { GivePlayerWeapon(killerid, 22, 50 } //if killer's rank is less than 10.
else if (gVar_Rank[killerid] == 10) { GivePlayerWeapon(killerid, 25, 50 } //if killer's rank is '10', it gives him a weapon with id 25 and 50 ammo.
else if (gVar_Rank[killerid] == 20) { GivePlayerWeapon(killerid, 25, 50 } //if killer's rank is '20', it gives him a weapon with id 25 and 50 ammo again.
return 1;
}