CIRCLES in BBC BASIC

You can "select, copy, paste" the programs on this page into

"BB4W"(BBC BASIC for WINDOWS) using the method shown here

A circle is easily plotted in BB4W (BBC Basic for Windows) using a programlet such as the following:

      MODE8:OFF
      CIRCLE 640,512,400

However, if we later wish to draw a spiral, it is necessary to start from a circle drawing program such as :

      MODE8:OFF
      ORIGIN 640,512
      R=300
      PLOT69,0,0
      MOVE R,0
      FOR t=0 TO 360
        DRAW R*COSRADt,R*SINRADt
        delay=INKEY(1)
      NEXT

Here:

R is the radius of the circle
t is the angle at the centre of the circle in degrees( measured anticlockwise from the right horizontal position)
RAD converts t into Radians (required before COSine and SINe can be computed)
delay is required so that you can see what is going on!
OFF turns off the flashing cursor
ORIGIN here specifies the graphics origin to be in the centre of the screen
MOVE here avoids a line being drawn from the centre to the start of the circle

Try changing a few of the parameters and see the effects (eg make R=something else). That's the way to "get a feel" for what is happening.

Here is a further program which will introduce you to applying colours, variable delays, and parameter display.

Richard Weston's Home Page