编程计算图形的面积。程序可计算圆形、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的值，计算出面积后将其显示出来-Programming calculate the area of ​ ​ the graph. The program calculates the area of ​ ​ the circular, rectangular, square, run first prompts the user to select the type of graphics, and then, the pair of circular require user input radius value to require user input the value of the length and width of the rectangle, to require user input side of square long value to calculate out area will be displayed