Circles; Plotting The Points Of A Circle - AMSTRAD cpc 6128 User Instruction

Circles
Circles can either be plotted or drawn. One method of forming a circle is to plot the
x,y, co-ordinates of each point on the circumference of a circle. Refer to the diagram
below and you will see that point 'p' on the circumference can be plotted using x and y
co-ordinates. These are:
x=19Ql*cos(a)
y=190*sin(a)
8
N
EDGE OF
I
SCREEN
320
Plotting the points of a circle.
In previous programs we have plotted points with respect to the bottom left corner of
the screen. Ifwe wanted to position a circle in the centre of the screen we would have
to plot the centre of the circle at co-ordinates 320,200 then position all points of the
circle relative to the centre position, by adding on the centre position co-ordinates.
A program to plot a circle would then be like this. Type in:
new
10 CLS
20 DEG
30 FOR a=1 TO 360
40 MOVE 320,200
50 DRAW 320+190*COS(a),200+190*SIN(a)
60 NEXT
run
Chapter 1 Page 60 Foundation Course
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