/in/foo.cc: In function 'int main()':
/in/foo.cc:18:22: error: 'scanf_s' was not declared in this scope
     scanf_s("%c", &ch);//吃掉n之后的换行符，vc使用scanf(),在vs2013中不安全，提示为scanf_s();
                      ^
/in/foo.cc:35:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i<v.size(); i++)
                      ^