fibonacci stage 1 spiral

%! % str1 str2 strcat -> concatstring % utility to concatenate strings /strcat { 5 dict begin /str2 exch def /str1 exch def /str1len str1 length def /str2len str2 length def /newstring str1len str2len add string def newstring 0 str1 putinterval newstring str1len str2 putinterval newstring end } def /fib { gsave 10 dict begin dup dup dup type cvlit str cvs (integertype) ne { (Argument to fib is not integer\n) show } { 1 lt exch 10 gt or {(Incoming argument for fib out of range\n) show } { % duplicate top of stack so it can be tested against % zero. If value is one pop the stack and then push 0 and 1 onto % stack and return, dup 1 eq { pop %pop incoming argument 0 1 } { %subtract 1 from value at top of stack for next recursive % call to fibb i.e. a call of fibb(i-1) 1 sub fib % now pick up two values returned on stack from level below and manipulate them dup 3 1 roll add } ifelse } ifelse % end of inrange check } ifelse % end of "is integer" check end grestore } def /Helvetica findfont 12 scalefont setfont /str 50 string def /xpos 250 def /ypos 470 def xpos ypos moveto 1 1 10 { dup dup xpos exch 20 mul ypos exch sub moveto str cvs (The value of fib ) exch strcat ( is ) str cvs strcat show % clean up the stack by deleting fibb(n-1) value -- the convert fibb(n) % value to a string fib exch pop str cvs show } for xpos 200 moveto % check that out of range value gives error message and then quits 0 fib xpos 180 moveto % test error message for non-integer argument 3.142 fib showpage