Function SetPlayerArmour set a player's armor level.
The function's name is armour, not armor (Americanized). This is inconsistent with the rest of SA-MP, so remember that.
Armour is obtained rounded to integers: set 50.15, but get 50.0

(playerid, Float:armour)
int playerid The ID of the player to set the armour of.
float armour The amount of armour to set, as a percentage (float). Values larger than 100 are valid, but won't be displayed in the HUD's armour bar.

Return Values:
  • 1: The function was executed successfully.
  • 0: The function failed to execute. This means the player specified does not exist.

public OnPlayerSpawn(playerid)
    // Give players full armour (100%) when they spawn.
    SetPlayerArmour(playerid, 100.0);
    return 1;

Related Functions
The following functions may be useful, as they are related to this function in one way or another.