new:Exercise 7-6. Write a program to compare two files, printing the first line where they differ.
improved:use ROLL instead of rand
new:Exercise 7-7. Modify the pattern finding program of Chapter 5 to take its input from a set of
named files or, if no files are named as arguments, from the standard input. Should the file
name be printed when a matching line is found?
improved:使m_getline能够读取各种输入
improved:改用fgets读行
learn:若一行的结尾是eof,fgets并不返回null,而是当再次读的时候再返回null
也就是说只有当读到的只有eof时才返回null