[Konstantinos]

PHP код:

public InBusinessCheck(playerid)
{
    Player[playerid][InBusiness] = -1;
    
    for(new i = 0; i < sizeof(Businesses); i++)
    {
        if(IsPlayerInRangeOfPoint(playerid, 3, Businesses[i][bInteriorX], Businesses[i][bInteriorY], Businesses[i][bInteriorZ]))
        {
            Player[playerid][InBusiness] = i;
            break;
        }
    }
    return 1;
} 


You set it to 0 at first and if the player is in range, it sets the new value and stops the loop otherwise (not in range of any business) it will remain 0.

EDIT: Actually 0 is a valid business ID so set it to -1. You must check if the variable is not -1 in case you use it in arrays though to prevent run time error 4.