new Float:checkpoints[4][4] =
{
{-2047.2,-83.0,34.8,3.0}, // DT1 and 24
{-2026.6925,-70.1228,34.8783,3.0}, // DT2
{-2004.7513,189.6104,27.2453,3.0}, // DT3
{-2005.5742,445.2907,34.7222,3.0} // DT4
};


if(strcmp,cmdtext,"/line",)
{
line[playerid]=1;
SetPlayerCheckpoint(playerid,checkpoints[1][0],checkpoints[1][1],checkpoints[1][2],checkpoints[1][3]);
return 1;
}
// LOL i just made that up so it might be wrong

and for the switch that i had wrong

public OnPlayerEnterCheckpoint(playerid)
{
        switch(line[playerid])
        {
       case 0:
       {
        //DoStuffHere
      }
      case 1:
      {
       //dostuffhere
}