C++ C++；cin输入问题

在下面的代码中，我遇到了cin问题。第一个cin执行得很好，但第二个根本不接收输入。我尝试了cin.clear（）来清除输入流，但没有任何帮助。据我所知，这是cin问题的常态

#include <iostream>
#include <string>
#include "StudentGradeInfo.h"

using namespace std;

const int MAX_NUM_GRADES=10;
const int MAX_NUM_STUDENTS=50;
const int STUD_ID_LENGTH=12;

int main(){

    char choice=' ';  //First user choice
    char choice_2=' ';  //second user choice
    string newStudentMajor;  //User inputted student major
    string studLastName;  //User inputted last name
    int newStudentID;  //User inputted student ID
    int studGrade;  //User inputted student grade
    int studentCounter=0;  //variable to count number of students

    //Allocating dynamic memory for MAX_NUM_STUDENTS student objects
    StudentGradeInfo *students=new StudentGradeInfo[MAX_NUM_STUDENTS];

    cout<<"Welcome to GradeBook, this program stores students"
    <<" grades by last name.  To ADD a student press the 'A'"
    <<" key.  To LIST all students, press the 'L' key.  To "
    <<" QUIT, press the 'Q' key."<<endl<<endl;

    cin>>choice;

    choice=toupper(choice);

    while(choice!='Q')  //While user does not decide to quit
    {
        if(choice=='A'&& studentCounter<MAX_NUM_STUDENTS){ //If user chooses to ADD
            cout<<"\nTo add a student, please enter their last name"
            <<" followed by a space and a non-negative grade"
            <<" Ex. Arthur 96"<<endl<<endl;
            cin>>studLastName>>studGrade;  //this cin works fine and using the 
                                                   //debugger I find that they contain
                                                   //the correct values
            cout<<cin.peek();  //Looking for chars left in input stream
            const char *charLastName=studLastName.c_str();
            int lastNameLength=studLastName.length();

            //Assign name to student object
            students[studentCounter].SetStudentName(charLastName, lastNameLength); 
            //Set Test Grade for student object
            students[studentCounter].SetStudentTestGrade(studGrade);

            cout<<"\nPlease enter the "<<STUD_ID_LENGTH<<"-digit Student ID followed by "
                <<"a space, then enter the student's major (Ex. 123456789012 Math)"<<endl;
            cin.clear();
            cin>>newStudentID>>newStudentMajor;  //User input
            cout<<newStudentID<<" "<<newStudentMajor;
            cout<<cin.peek();  //Checking for chars left in input stream
            //Adding ID and Major to students object.
            students[studentCounter].SetStudentID(newStudentID); 
            students[studentCounter].SetStudentMajor(newStudentMajor); 
            cout<<students[studentCounter].GetStudentID();
            cout<<"\nWould you like to enter more grades for this "
            <<"student? If yes, please enter 'Y', if no, "
            <<"enter 'N'"<<endl;

            cin>>choice_2;
            choice_2=toupper(choice_2);  //Upper-case conversion

            while(choice_2!='N'){
                if(choice_2=='Y'){
                    cout<<"\nPlease enter a grade followed by pressing "
                    <<"enter.\n";

                    for(int i=0;i<MAX_NUM_GRADES;i++){ //Inputting grades for individual
                        cin>>studGrade;           //student
                        if(studGrade==-1) //Condition for premature loop exit
                            break;
                        students[studentCounter].SetStudentTestGrade(studGrade); //Add Grade
                        cout<<"\nWould you like to add another grade? "
                        <<"If so, enter the next grade.  Otherwise"
                        <<" enter -1 to return to the menu"<<endl;
                    }
                    cout<<"This student currently has the maximum number of grades. \n";
                    break;
                }//If answer yes is chosen
                else if(choice_2!='N'&& choice_2!='Y'){  //If wrong character is input
                    cout<<"\nPlease enter either 'Y' or 'N'"<<endl;
                    cin>>choice_2;
                    choice_2=toupper(choice_2); //Upper-case conversion
                }
            }//While choice_2!='N'
            students[studentCounter].SortStudentID(students);
            studentCounter++;  //Incrementing studentCounter after all possible changes have
                               //been made to that student
        }

        else if(choice=='L'){  //If user decides to list
            cout<<"GRADEBOOK \n------------------------------\n";

            for(int i=0; i<studentCounter; i++){  //Such a better solution than last gradebook
                cout<<"\nentering list loop \n";
                cout<<students[i];  //Overloaded insertion operator, outputs all student information

            }   
        }

        else if(choice!='Q')  //If user inputs invalid character
            cout<<"Your letter is invalid, please enter another letter"<<endl<<endl;

        cout<<"\nTo ADD a student press the 'A' key.  To LIST all students, press the 'L' key. "
        <<"  To QUIT, press the 'Q' key."<<endl<<endl;      

        cin>>choice;
        choice=toupper(choice); //Upper-case conversion
    }
}

#包括
#包括
#包括“StudentGradeInfo.h”
使用名称空间std；
const int MAX_NUM_GRADES=10；
const int MAX_NUM_STUDENTS=50；
const int STUD_ID_LENGTH=12；
int main（）{
char choice=''；//第一个用户选择
char choice_2=''；//第二个用户选择
字符串newStudentMajor；//用户输入的学生专业
string studLastName；//用户输入的姓氏
int newStudentID；//用户输入的学生ID
int studGrade；//用户输入的学生成绩
int studentCounter=0；//用于计算学生人数的变量
//为MAX_NUM_student学生对象分配动态内存
StudentGradeInfo*students=new StudentGradeInfo[MAX_NUM_students]；
cout您的学生ID是12位长度。没有12位十进制值适合32位整数。请尝试将其存储在字符串中。
对不起，我现在没有时间调试此项，但我猜：学生ID不适合
int
。您能将STUD\u ID\u长度减少到6并重新运行您的实验吗？在我的作业中，它是有效的（是的，这是家庭作业）它需要12位数字。我怎么做？将学生ID存储在
std:：string
中，而不是
int
。应该可以。谢谢。如果你想回答它，我会给你，
操作符==（StudentGradeInfo&，StudentGradeInfo&）
将因堆栈溢出而死亡。
#include <iostream>
#include <string>
#include "StudentInfo.h"

using namespace std; 

const int STUDENT_ID_LENGTH=12;

    //default constructor
StudentInfo::StudentInfo()
{
}
//Parameterized constructor
StudentInfo::StudentInfo(string newStudentName, int newStudentID, string newStudentMajor)
{
    int nameLength=newStudentName.length();
    char *nameArray=new char[nameLength];

    SetStudentName(nameArray, nameLength);
    SetStudentID(newStudentID);
    SetStudentMajor(newStudentMajor);
}

StudentInfo::~StudentInfo()  //Destructor
{ 
    delete[] studentName;  //deallocating dynamic memory 
}

//Member functions for initializing and displaying private data
//pre: array of characters and a positive int for nameLength
//post: studentName contains name of new student
void StudentInfo::SetStudentName(const char newStudentName[], int lastNameLength)
{
    char *studentName=new char[lastNameLength];

    for(int i=0; i<lastNameLength; i++){
        studentName[i]=newStudentName[i];
    }
}

//post: Returns name of student
string StudentInfo::GetStudentName() const
{
    return studentName;
}

//pre: positive integer input
//post: studentID contains newStudentID or msg is displayed that ID is invalid
void StudentInfo::SetStudentID(int newStudentID)
{
    double new_ID;
    int divisionsCount=0;
    new_ID=newStudentID;
    while(new_ID>1){
        new_ID=new_ID/10;
        divisionsCount++;
    }

    if(divisionsCount!=STUDENT_ID_LENGTH){
        cout<<"ID is not "<<STUDENT_ID_LENGTH<<" characters long\n";
        return;
    }
    studentID=newStudentID;
}
//pre: valid integer for studentID
//post: returns integer to caller
int StudentInfo::GetStudentID() const
{
    return studentID;
}

//pre: String type of student Major and newStudentMajor
//post: studentMajor contains newStudentMajor string
void StudentInfo::SetStudentMajor(string newStudentMajor)
{
    studentMajor=newStudentMajor;
}

//post: returns string studentMajor
string StudentInfo::GetStudentMajor() const
{
    return studentMajor;

#include <string>  //including string data type
#include <iostream>
#include "StudentGradeInfo.h"

using namespace std; 

StudentGradeInfo::StudentGradeInfo():StudentInfo()
{
    //StudentInfo::StudentInfo();
    gradeCounter=0;
}

//Parameterized Constructor
StudentGradeInfo::StudentGradeInfo(string &newStudentName, int &newStudentID, 
                string &newStudentMajor, int newTestGrade, double newtestAverage, int newGradeCounter): 
                StudentInfo(newStudentName, newStudentID, newStudentMajor)
{
    gradeCounter=0;
    SetStudentTestGrade(newTestGrade);
}

//pre: positive integer input
//post: testGrade contains newTestGrade or msg is displayed that the score is invalid or contains max # of grades
void StudentGradeInfo::SetStudentTestGrade(int newTestGrade)
{
/*  if(gradeCounter>MAX_NUM_GRADES){  //If the maximum number of grades has been reached
        cout<<"\nThis student currently has the maximum number of grades.";  //Inform user
        return;                         //Leave function and not assign input grade
    }*/
    testGrade[gradeCounter]=(newTestGrade > 0 && newTestGrade<=100) ? newTestGrade : -1; //Grade assignment
    if(testGrade[gradeCounter]!=-1)                                                     //and validity testing
        gradeCounter++;    //Increment number of grades this student has
    else
        cout<<endl<<testGrade[gradeCounter]<<" is not a valid score.\n"; //Inform user which score was invalid
}

//pre: positive integer
//post: returns testGrade found in that array
int StudentGradeInfo::GetStudentTestGrade(int gradeNum) const
{
    if(gradeNum>=0 && gradeNum<=MAX_NUM_GRADES) //If gradeNum is a valid grade and not stepping off of array 
        return testGrade[gradeNum];
    else
        return 0;
}

//post: testAverage is calculated
void StudentGradeInfo::SetTestAverage()
{
    int num_Sum;
    for(int i=0;i<gradeCounter;i++)
        num_Sum+=testGrade[i];  //summing total grades
    testAverage=(num_Sum/(gradeCounter+1));  //Calculating average
}

//post: returns calculated testAverage double
double StudentGradeInfo::GetTestAverage()
{
    SetTestAverage();
    return testAverage;
}

//pre: initialized StudentGradeInfo object array
//post: Students are sorted by studentID
void StudentGradeInfo::SortStudentID(StudentGradeInfo newStudent[])
{
    int tempValue;

    while(IDSorted(newStudent)!=true){  //If students are not sorted
        for(int i=0; i<(gradeCounter-1); i++){
            //Determining if these two students need switched
            if(newStudent[i].GetStudentID()<=newStudent[i+1].GetStudentID()) 
                continue;  //If they don't need switched, continue
            else{  //Otherwise switch the two students
                tempValue=newStudent[i+1].GetStudentID();
                newStudent[i+1].SetStudentID(newStudent[i].GetStudentID());
                newStudent[i].SetStudentID(tempValue);
            }
        }
    }
}

//pre: initialized StudentGradeInfo object array
//post: returns true if newStudent array has been sorted by studentID, false otherwise
bool StudentGradeInfo::IDSorted(StudentGradeInfo newStudent[])
{
    for(int i=0; i<(gradeCounter-1);i++){  //Determining if array is sorted from smallest to largest
        if(newStudent[i].GetStudentID()<=newStudent[i+1].GetStudentID()) 
            continue;
        else
            return false;
    }
    return true;
}

//Overloaded insertion operator to output entire students information
ostream &operator<<(ostream &output, StudentGradeInfo &newStudent)
{
    output<<"This is the student major: "<<newStudent.GetStudentMajor();

    output<<"__________________________________\n"
          <<"Name: "<<newStudent.GetStudentName()<<"\nID: "<<newStudent.GetStudentID() //outputs studentID and name
          <<"\nMajor: "<<newStudent.GetStudentMajor()<<"\nGrades: ";        //outputs studentMajor
    for(int i=0;i<newStudent.gradeCounter;i++)
        output<<newStudent.testGrade[i]<<" ";  //outputs studentGrade's 
    output<<"Grade Average: "<<newStudent.GetTestAverage();
    return output;
}

bool operator==(StudentGradeInfo &newStudent_One, StudentGradeInfo &newStudent_Two)
{
    if(newStudent_One==newStudent_Two)  //testing for equality
        return true;
    else
        return false;
}
    }