How can i develop a graphic shape which depends on user input

How can i draw a shape of circle which depends on user input.for example if i give input as 10 a circle of radius 5 should be drawn and when i give as 20 then the circle should increase its size automatically.I want these changes to be done at runtime.input should also be given at runtime

[303 byte] By [camel10] at [2007-9-26 4:30:19]