TEX Quotes

Think:
引号转换题，　因为不知道长度，所以用getchar（）
但是不明白　为什么代码　在编译器上会　报错。。。
但是　提交是ＡＣ的。。
所以思路就是，读取字符然后判断时候是 ” ，　如果是的话在判断
是第几次出现（也就是判断　是左　还是　右　引号），然后　改变
输出字符。
题目虽然很长　但是是水题　。。。

Problem Description
TEX is a typesetting language developed by Donald Knuth. It takes source text together with a few typesetting instructions and produces, one hopes, a beautiful document. Beautiful documents use double-left-quote and double-right-quote to delimit quotations, rather than the mundane ” which is what is provided by most keyboards. Keyboards typically do not have an oriented double-quote, but they do have a left-single-quote and a right-single-quote '. Check your keyboard now to locate the left-single-quote key (sometimes called the “backquote key”) and the right-single-quote key ’ (sometimes called the “apostrophe” or just “quote”). Be careful not to confuse the left-single-quote ` with the “backslash” key . TEX lets the user type two left-single-quotes “ to create a left-double-quote and two right-single-quotes ” to create a right-double-quote. Most typists, however, are accustomed to delimiting their quotations with the un-oriented double-quote “.

If the source contained
“To be or not to be,” quoth the bard, “that is the question.”
then the typeset document produced by TEX would not contain the desired form: “To be or not to be,” quoth the bard, “that is the question.” In order to produce the desired form, the source file must contain the sequence:
To be or not to be,'' quoth the bard,that is the question.”
You are to write a program which converts text containing double-quote (“) characters into text that is identical except that double-quotes have been replaced by the two-character sequences required by TEX for delimiting quotations with oriented double-quotes. The double-quote (“) characters should be replaced appropriately by either if the " opens a quotation and by '' if the " closes a quotation. Notice that the question of nested quotations does not arise: The first " must be replaced by, the next by ”, the next by , the next by '', the next by, the next by ”, and so on.

Input
Input will consist of several lines of text containing an even number of double-quote (“) characters. Input is ended with an end-of-file character.

Output
The text must be output exactly as it was input except that:

the first " in each pair is replaced by two ` characters: `` and the second " in each pair is replaced by two ' characters: ''. 

Sample Input

“To be or not to be,” quoth the Bard, “that
is the question”.
The programming contestant replied: “I must disagree.
To C' or not toC’, that is The Question!”

Sample Output

To be or not to be,'' quoth the Bard,that
is the question”.
The programming contestant replied: `I must disagree.
ToC’ or not to `C’, that is The Question!”

题目大意：
１．给定字符串
２．将左”转换成“　将右”转换成’ ‘;

 #include<bits/stdc++.h>    using namespace std;      int main()      {          char a ;          int flag = 0;          while((a = getchar())!=EOF)          {              if(a == '"'&& flag == 0)              {                  printf("``");                  flag = 1;              }              else if(a == '"' && flag == 1)              {                  printf("''");                  flag = 0;              }              else              {                  printf("%c",a);              }          }      }