在下面的代码中，我遇到了cin问题。第一个cin执行正常，但第二个cin完全没有接收输入。我已经尝试过cin.clear（）来清除输入流，但它没有帮助。根据我的理解，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
}
}
StudentInfo.cpp
#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;
StudentGradeInfo.cpp
#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;
}
}
提前致谢
答案 0 :(得分：2)
您的学生证长度为12位数。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。