设计一个简单的MFC程序，该程序在鼠标左键单击位置画一个矩形，矩形的大小是随机的。设计思路：(1)在程序中定义一个矩形数组，用来存放随机生成的矩形。(2)以鼠标单击位置为中心，以随机函数rand()产生的数为边长生成一个矩形，并将此矩形保存在矩形数组中。(3)然后产生一条WM_PAINT消息，并在相应的消息处理函数中重绘数组中的所有矩形。（源代码中有非常完整的注释，方便读者理解程序）-Design a simple MFC program, which position the mouse left click to draw a rectangle, rectangle size is random. Design: (1) in a program to define a rectangular array, used to store a randomly generated rectangle. (2) to the mouse click position as the center, random function rand () produces a number of side length generates a rectangle and rectangle stored in a rectangular array. (3) and then generates a WM_PAINT message, and in the corresponding message handler redraw all the rectangles in the array. (Source code for a very complete notes to facilitate readers to understand the program)