// ( Check if a_samp it's included in the main script )
#if !defined a_samp

#include a_samp

#endif
#if !defined foreach

#include foreach

#endif

#define FLOAT_INFINITY (Float:0x7F800000)

// ( This is the function you can simply use on your script )
stock GetClosestPlayer( playerid, checkvw = false, Float:range = FLOAT_INFINITY )
{
    new Float:playerPos[ 3 ], Float:thisDist;
    GetPlayerPos( playerid, playerPos[ 0 ], playerPos[ 1 ], playerPos[ 2 ]);

    new Float:closestDist = FLOAT_INFINITY;
    new closestPlayer = INVALID_PLAYER_ID;

    foreach(new i : Player)
    {
        if( i == playerid ) continue;
        if( checkvw && GetPlayerVirtualWorld( playerid ) != GetPlayerVirtualWorld( i ) ) continue;
        if( GetPlayerInterior( playerid ) != GetPlayerInterior( i ) ) continue;

        thisDist = GetPlayerDistanceFromPoint( i, playerPos[ 0 ], playerPos[ 1 ], playerPos[ 2 ] );
        if( thisDist < closestDist && thisDist < range )
        {
            closestPlayer = i;
            closestDist = thisDist;
        }
    }
    return closestPlayer;
}