4 rem *** DRAWING AREA SETUP ***
5 scnclr
10 input "enter screen x coord of origin (default 320): ",xs
20 input "enter screen y coord of origin (default 200): ",ys
30 input "enter zoom (default 1): ",z
31 if z<=0 then print "": print "zoom must be >0, please enter the correct value": goto 30
32 xp=-30000 : rem dummy previous X value
33 yp=-30000 : rem dummy previous X value
34 xr=320/z : rem RANGE defined as nominal X resolution divided by zoom

39 rem *** DRAWING AREA IS BEING DRAWN ***
40 graphic clr
50 screen def 1,1,1,4: rem screen def 1,0,0,4
60 screen open 1
70 palette 1,0,0,0,0 :     rem black
80 palette 1,1,15,0,0 :    rem red
90 palette 1,2,0,0,15 :    rem blue
100 palette 1,3,0,15,0 :   rem green
110 palette 1,4,15,11,0 :  rem orange
120 palette 1,5,0,11,15 :  rem dark cyan
121 palette 1,6,15,15,15 : rem white
122 palette 1,7,15,15,0 :  rem yellow
123 palette 1,8,7,7,7 :    rem medium gray
130 screen set 1,1
140 scnclr 2
150 border 2

270 rem *** CARTESIAN AXES ARE BEING DRAWN (FROM -3000 TO 3000) ***
280 pen 0,6
285 rem *** VERTICAL (Y) AXIS
290             x=0: y=0-3000: gosub 1000
300 x0=x: y0=y: x=0: y=3000: gosub 1000
310 x1=x: y1=y: line x0,y0,x1,y1
315 rem *** HORIZONTAL (X) AXIS ***
320             x=0-3000: y=0: gosub 1000
330 x0=x: y0=y: x=3000: y=0: gosub 1000
340 x1=x: y1=y: line x0,y0,x1,y1
341 pen 0,7
420 gosub 2000
500 gosub 5090



1000 rem CARTESIAN COORDINATES TO SCREEN COORDINATES
1001      x=x*z
1002      y=y*z
1010      x=x+xs
1020      y=ys-y
1030      return

2000 rem PLOT THE FUNCTION
2001 st=1/z : rem the STEP is the inverse of the zoom
2010      for x0=-xs to xs step st
2020          y0=sin(x0)
2021          y1=tan(x0)
2022          y0=y0*y1 : rem y0=sin(x0)*tan(x0)
2030          x=x0
2031          y=y0
2040          gosub 1000
2050          rem draw x,y
2051          rem print x,y
2055          line xp,yp,x,y
2056          xp=x: yp=y
2060      next x0



5090 get a$
5100 if a$ = "" then goto 5090
5110 screen close 1
5120 palette restore
5130 border 6