1.　　编写一个使用指针返回类型的函数，使用该函数在字符串中搜索一个子串，并返回第一个相匹配的子串指针。该函数的原型如下：

输入为3行。第一行为两个整数，表示字符串和需要查找的子串的长度。第二行为字符串，第三行为子串。

输出见main函数。

程序的一个输入输出样例为：

Enter the length of string and substring

10 5

abcdefghij

defgh

find substring:defghij

-1. Write a function that returns a pointer to the type of use, use the search function is a substring in the string, and returns the first match substring pointer. The prototype of this function is as follows: Input for 3 rows. The first acts of the two integer representing the length of the string and the need to find a substring. The second behavior string substring third acts. Output, see the main function. An input and output sample program is: Enter the length of string and substring 10 5 abcdefghij defgh find substring: defghij