program-id.y.data division.working-storage section.
1 i pic 9.
1 j pic 999.
1 k pic 9.
1 n pic 9.
procedure division.accept n
display"Gray code  n="n.a.move n to i.b.compute k=function mod(.5+j/2^i,2)display k no advancing
if i>1 add -1to i go b.display""add 1 to j if j<2^n go a.