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代码说明：

说明：  设计一个函数，其功能是同时求得长度为20的整型数组所有元素中的最大值、最小值和平均值。并用相应的主函数对其进行测试，测试数组可以用随机数填充或者自行定义数据。(The design of a function, its function is to obtain the length of the maximum, minimum and average 20 integer array element. And its main function testing, the test array can be populated with a random number or define your own data.)