画板，在画板上画图形。 提供了撤销和恢复的功能，提供了存放命令的面板，放置画圆、画线等命令的按钮。-Sketchpad, in the Sketchpad drawing graphics. Provided the revocation and restoration of function, provides a storage panel orders placed drawcircle, painting lines command button.

本程序是程序设计第五版课后习题,实现画圆,画直线,画矩形,并且可以填充.-This procedure is the fifth edition of the after-school exercise program design, implementation drawcircle, draw a straight line, draw rectangle and can be filled.