在C语言里面一直很容易混淆的，gets和fgetS的区别：
char * fgets ( char * str, int num, FILE * stream );
Reads characters from stream and stores them as a C string into str until (num-1) characters have been read or either a newline or the end-of-file is reached, whichever happens first.
A newline character makes fgets stop reading, but it is considered a valid character by the function and included in the string copied to str.
A terminating null character is automatically appended after the characters copied to str.
Notice that fgets is quite different from gets: not only fgets accepts a stream argument, but also allows to specify the maximum size of str and includes in the string any ending newline character.
char * gets ( char * str );
Get string from stdin
Reads characters from the standard input (stdin) and stores them as a C string into str until a newline character or theend-of-file is reached.
The newline character, if found, is not copied into str.
A terminating null character is automatically appended after the characters copied to str.
Notice that gets is quite different from fgets: not only gets uses stdin as source, but it does not include the ending newline character in the resulting string and does not allow to specify a maximum size for str (which can lead to buffer overflows).
简单说来，fgets能够指定最大输入字符数(num - 1)，他们都在遇到换行符的之后终止，fgets把换行符也读进字符串里，gets简单的丢掉换行符。
C++中对应的有cin的四个函数：
istream & get(char *, int, char);
istream & get(char *, int);
istream & getline(char *, int, char);
istream & getline(char *, int);
这里，get和getline都不会把换行符读进去，但是get会把换行符（或者指定的其他分隔符）留在流里面，而getline会把换行符从流中读取出来并丢弃。
