给定程序MODI1.C中函数fun的功能是：统计substr所指字符串在str所指字符串中出现的次数。

例如，若字符串为aaas lkaaas,子字符串为as，则应输出2.

请改正程序中的错误，使它能计算出正确的结果。

注意：不要改动main函数，不得增行或删行，也不得更改程序的结构。-In a given program MODI1.C function fun is the function: Statistics within the meaning of the string substr in string str within the meaning of the number of occurrences. For example, if the string is aaas lkaaas, sub-string as, should the output 2. Please correct the errors in the program, so that it can calculate the correct results. Note: Do not change the main function, not by lines or delete lines, nor change the structure of the program.