Hi, I am trying to understand a code written by different author so that I can modify it for my purpose. However, since my experience with IDL is limited and I am trying to learn on my own, I am not able to understand some of the syntax or statement. Please click here: http://idlastro.gsfc.nasa...p/pro/fits/sxpar.pro sxpar.pro: I am not able to understand the statements on line 184 and 190. I would really appreciate if somebody can explain it to me. Statement on line 184: if vector then begin Statement on line 190: if VALID_NUM( numst[i], num,/INTEGER) then number[i] = num Thanks , Dushyant Kumar