一个有趣的小问题

iwaich

// Define class GradeBook that contains a courseName data member
// and member functions to set and get its value;
// Create and manipulate a GradeBook object.
#include <iostream>
using std::cout;
using std::cin;
using std::endl;

#include <string> // program uses C++ standard string class
using std::string;
using std::getline;

// GradeBook class definition
class GradeBook
{
public:
   // function that sets the course name
   void setCourseName( string name )
   {      
      courseName = name; // store the course name in the object
   } // end function setCourseName
   
   // function that gets the course name
   string getCourseName()
   {
      return courseName; // return the object's courseName
   } // end function getCourseName

   // function that displays a welcome message
   void displayMessage()
   {
      // this statement calls getCourseName to get the
      // name of the course this GradeBook represents
      cout << "Welcome to the grade book for\n" << getCourseName() << "!"
         << endl;
   } // end function displayMessage
private:
  string courseName;// course name for this GradeBook
}; // end class GradeBook  

// function main begins program execution
int main()
{string nameOfCourse; // string of characters to store the course name
   GradeBook myGradeBook; // create a GradeBook object named myGradeBook
   
   // display initial value of courseName
   cout << "Initial course name is: " << myGradeBook.getCourseName()
      << endl;

   // prompt for, input and set course name
   cout << "\nPlease enter the course name:" << endl;
   getline(cin, nameOfCourse ); // read a course name with blanks
   myGradeBook.setCourseName( nameOfCourse ); // set the course name

   cout << endl; // outputs a blank line
   myGradeBook.displayMessage(); // display message with new course name
   
   return 0; // indicate successful termination
} // end main

这是一个从书上拷下来的代码，运行到 getline(cin, nameOfCourse );
要求我输入课程名，可是为什么输入之后要按两个回车，程序才继续执行，应该一个回车就可以了啊。不知道为什么，你们看看!