（1）用Bresenham算法绘制直线 （2）程序适用各种直线情况，包括水平线，垂直线 （3）采用键盘输入线段的两个端点的坐标 -(1) using Bresenham algorithm for drawing a straight line (2) procedure applies to all kinds of straight lines, including horizontal, vertical lines (3) the use of keyboard input