The Ball Demonstration Program
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The Ball program simulates a series of bouncing balls. A
variable named "grid" displays as a two-dimensional grid on
which the balls bounce. The balls are represented using an array
of ASCII characters. 

Three kinds of balls are simulated:
*  *A soft ball:* This ball bounces off walls. The soft ball does
   not affect the other balls it collides with. The soft ball is
   represented by the character '0'.
*  *A hard ball:* This ball deflects any ball it collides with. It is
   represented by the character '*'.
*  *A spinning ball:* This ball deflects and turns any ball it collides with. 
   It is represented by the character '@'.

