Source code in the action! programming language

PROC Swap(BYTE ARRAY tab INT i,j)
  BYTE tmp

  tmp=tab(i) tab(i)=tab(j) tab(j)=tmp
RETURN

BYTE FUNC QuickSelect(BYTE ARRAY tab INT count,index)
  INT px,i,j,k
  BYTE pv

  DO
    px=count/2
    pv=tab(px)
    Swap(tab,px,count-1)
    
    i=0
    FOR j=0 TO count-2
    DO
      IF tab(j)
        Swap(tab,i,j)
        i==+1
      FI
    OD

    IF i=index THEN
      RETURN (pv)
    ELSEIF i>index THEN
      ;left part of tab from 0 to i-1
      count=i
    ELSE
      Swap(tab,i,count-1)
      ;right part of tab from i+1 to count-1
      tab==+(i+1)
      count==-(i+1)
      index==-(i+1)
    FI
  OD
RETURN (0)

PROC Main()
  DEFINE COUNT="10"
  BYTE ARRAY data=[9 8 7 6 5 0 1 2 3 4],tab(COUNT)
  BYTE i,res

  FOR i=0 TO COUNT-1
  DO
    MoveBlock(tab,data,COUNT)
    res=QuickSelect(tab,COUNT,i)
    PrintB(res) Put(32)
  OD
RETURN