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代码说明：

说明：  编程计算图形的面积。程序可以计算圆形，长方形，正方形的面积，运行时先提示用户选择图形的类型，然后，对圆形要求用户输入半径值，对长方形要求用户输入长和宽的值，对正方形要求用户输入边长得值，计算出面积的值后将其显示出来。(Calculate the area of graphics programming. Program can calculate the round, rectangular, square area, run-time prompts the user to first select the type of graph, and then the radius of the circle requires the user to input the value of the rectangle requires the user to input the length and width values, requires the user to input side of the square grow the value to calculate the value of the area after the show.)