函数的嵌套调用和递归调用，函数的嵌套调用, 求三个数中最大数和最小数的差值。运行结果： 5 -6 15↙ 21 -Nested function calls and recursive calls, nested function calls, find the maximum number of three numbers and the minimum number of difference. The result: 5-6 15 ↙ 21