I've been doing c++ self study after taking two semesters of Java.
Below is a simple program which builds fine, but when I run it I get gradeBook2s displayInfo() method called twice. I'm sure its something basic I am missing, but any ideas why?
//GradeBook.h
#include<string>
#include<iostream>
using std::cout;
using std::endl;
using std::string;
string courseName;
int courseGrade;
class GradeBook {
public:
GradeBook(string name, int grade) {
setCourseName(name);
setCourseGrade(grade);
}
public:
void setCourseName(string name) {
courseName = name;
}
public:
string getCourseName() {
return courseName;
}
public:
void setCourseGrade(int score) {
courseGrade = score;
}
public:
int getCourseGrade() {
return courseGrade;
}
public:
void displayInfo(){
cout << "Course Name: " << getCourseName()
<< "Course grade: " << getCourseGrade()
<< endl;
}
};
//main.cpp
#include<iostream>
#include "GradeBook.h"
int main() {
GradeBook gradeBook1("Calculus 2", 90);
GradeBook gradeBook2("Chemistry", 80);
gradeBook1.displayInfo();
system("pause");
gradeBook2.displayInfo();
system("pause");
}
The problem that you have is that you are saving the variables courseName and courseGrade as global variables. Because of this, you are overwriting the previous class instance's data with the current, in this case, Chemistry. What you need to do is move the declaration of courseName and courseGrade inside the accessor private inside the class, like this:
class GradeBook {
private:
string courseName;
int courseGrade;
public:
//put your functions here
}
The locations where the code stores values is global, so all instances will appear the same.
Related
I have a homework task with a given main.cpp code which is not allowed to be changed. According to that main.cpp and simple input and output(which is down below) example I must to finish the program.
My tries are: I'm trying to create 4 classes, class Person; class Worker; class Student; class InService; in my main function through instantiating an object of InService class I pass 4 parameters (name, sex, studentNo, workerNo); and with help of pointer of type of Base class, have the desired output. The error it shows is:
[Error] no unique final overrider for 'virtual std::string Person::getName()' in 'InService'
[Error] no unique final overrider for 'virtual int Person::getSex()' in 'InService'
I've tried to use virtual inheritance for that, but I can't really figure out how to solve this problem. I did some research on virtual inheritance, and referenced to other experts answers, but still getting confused with whole OOP stuff.
//Inservice.h
#include<string>
using namespace std;
class Person{
public:
Person();
~Person();
string name;
int sex;
virtual string getName() = 0;
virtual int getSex() = 0;
};
///////////////////////////////////////////////////
class Student:virtual public Person{
public:
Student();
~Student();
string sno;
virtual string getName() {
return name;
}
virtual int getSex(){
return sex;
}
string getSno(){
return sno;
}
};
//////////////////////////////////////////////////
class Worker:virtual public Person{
public:
Worker();
~Worker();
string wno;
virtual std::string getName(){
return name;
}
virtual int getSex(){
return sex;
}
string getWno(){
return wno;
}
};
///////////////////////////////////////////////////////
class InService: public Student, public Worker{
public:
InService(string _name, int _sex, string _sno, string _wno){
Person::name = _name;
Person::sex - _sex;
Worker::wno = _wno;
Student::sno = _sno;
}
};
///////////////////////////////////////////////////////
//main.cpp
#include <iostream>
#include "inservice.h"
using namespace std;
int main() {
string name, sno, wno;
int sex;
cin >> name;
cin >> sex;
cin >> sno;
cin >> wno;
InService is(name, sex, sno, wno);
Person* p = &is;
Student* s = &is;
Worker* w = &is;
cout << p->getName() << endl;
cout << p->getSex() << endl;
cout << s->getName() << endl;
cout << s->getSex() << endl;
cout << s->getSno() << endl;
cout << w->getName() << endl;
cout << w->getSex() << endl;
cout << w->getWno() << endl;
return 0;
}
Suppose my input is:
Jack
1 //1-for male; 0 -for female
12345678 //studentNo
87654321 //workerNo
I expect the output to be:
Jack
1
12345678
Jack
1
87654321
InService(string _name, int _sex, string _sno, string _wno){
Person::name = _name;
Person::sex - _sex;
Worker::wno = _wno;
Student::sno = _sno;
}
There's a typo there, Person::sex - _sex; should be Person::sex = _sex;
Also you can remove name and sex virtual function and have it just a standard function in Person, since it's exactly the same for all classes that derive from it. That will remove the ambiguity of which getName and getSex function that InService class virtual table needs to point to.
I have this requirement.
I am trying to make a simple database schema, a little different than what I have seen in here. I have a class file (client.h) with it's implementation (client.cpp):
#ifndef CLIENT_H_
#define CLIENT_H_
#include <iostream>
using namespace std;
class Client {
public:
// constructors
Client();
Client(string new_name, string new_tel, string new_addr);
// getters
string getName();
string getAddr();
string getTel();
// setters
void setName(string);
void setAddr(string);
void setTel(string);
void display();
void input();
private:
// fields
string name;
string addr;
string tel;
};
#endif /* CLIENT_H_ */
/*
*ad client.cpp
*
* Created on: Jan 12, 2017
* Author: niksarid
*/
#include <iostream>
#include "client.h"
using namespace std;
Client::Client() {
setName("");
setAddr("");
setTel("");
}
Client::Client(std::string new_name, std::string new_addr, std::string new_tel) {
setName(new_name);
setAddr(new_addr);
setTel(new_tel);
}
string Client::getName() {
return name;
}
string Client::getAddr() {
return addr;
}
string Client::getTel() {
return tel;
}
void Client::setName(string p_name) {
name = p_name;
}
void Client::setAddr(string p_addr) {
addr = p_addr;
}
void Client::setTel(string p_tel) {
tel = p_tel;
}
void Client::input() {
string tmp;
cout << "INPUT CLIENT INFO" << endl;
cout << "Name: ";
cin >> tmp;
setName(tmp);
cout << "Address: ";
cin >> tmp;
setAddr(tmp);
cout << "Telephone: ";
cin >> tmp;
setTel(tmp);
}
void Client::display() {
cout << name << "\t" << addr << "\t" << tel << endl;
}
So I am trying to make a Company class that will hold a vector of Clients and at the startup of the program it will load the datafile "clients.dat", into the vector. I will be able to add a client or delete a client from the vector. At the end the vector will be saved back to "clients.dat".
So, the (company.h) file is like this:
class Company {
public:
Company();
~Company();
void add_client();
void print_clients();
void loadClientsFromFile();
void saveClientsToFile();
private:
vector<Client> clients;
} cmp;
#endif /* COMPANY_H_ */
but I can't seem to reference clients vector in any of the public methods of the class company.
EDIT: Sorry! Forgot the important part!!
For example when I try to add_client(),
void add_client() {
Client c;
c.input();
clients.push_back(c);
}
but I get
../src/company.cpp:49:2: error: 'clients' was not declared in this scope
clients.push_back(c);
So, how to achieve that?
As Morgan mentioned in the comments, this problem typically arises when you try to define the member function in your implementation file, but forget to add the class name as prefix (e.g. void add_client() {} instead of void Company::add_client() {}.
This mistake is common and can easily go unnoticed, since it is perfectly legal to define a new free function called add_client in your file, that would have nothing to do with the Company class. That's why the compiler only complains when you try to access a data member, but not before.
I have to create a small console application in C++ which will do the following:
Create class Subject which has next attributes: name of the subject, number of students and array of students who are attending that subject. After that createa class Student which has name and surname of the student as attributes. In Main file count how many duplicate names there are in each Subject.
I have few problems here. First one is that I don't know how to initialize an array in my Subject.h file. Second is how to actually put Student objects into Subject objects and compare the names in the end.
What I'd like output to look like:
Duplicate names in subjectA are: Michael.
Duplicate names in subjectB are: Nicholas, John.
Where subjectA and subjectB should be called C++ and C.
Here is my code so far (I googled for past hour or two about this problem of mine but I just couldn't find a proper answer/example).
NOTE: I'm including all these files for clarification.
Subject.h
#include <string>
#include <iostream>
using namespace std;
/*
* I should also have an array named `arrayOfStudents`
* which should store all students who are attending
* that Subject.
*/
class Subject
{
public:
Subject();
Subject(Subject &subject);
Subject(string nameOfSubject, int numberOfStudents);
~Subject();
const string getNameOfSubject();
const int getNumberOfStudents();
void setNameOfSubject(string nameOfSubject);
void setNumberOfStudents(int numberOfStudents);
void print();
private:
string nameOfSubject;
int numberOfStudents;
};
Subject.cpp
#include <iostream>
#include "Subject.h"
using namespace std;
Subject::Subject()
{
}
Subject::Subject(string nameOfSubject, int numberOfStudents)
{
this->nameOfSubject = nameOfSubject;
this->numberOfStudents = numberOfStudents;
}
Subject::Subject(Subject &Subject) : nameOfSubject(Subject.getNameOfSubject()), numberOfStudents(Subject.getNumberOfStudents())
{
}
Subject::~Subject()
{
cout << "Object is destroyed" << endl;
}
const string Subject::getNameOfSubject()
{
return nameOfSubject;
}
const int Subject::getNumberOfStudents()
{
return numberOfStudents;
}
void Subject::setNameOfSubject(string nameOfSubject)
{
nameOfSubject = this->nameOfSubject;
}
void Subject::setNumberOfStudents(int numberOfStudents)
{
numberOfStudents = this->numberOfStudents;
}
void Subject::print()
{
cout << "Subject: " << nameOfSubject << " :: Number of students: " << numberOfStudents << endl;
}
Student.h
#include <string>
#include <iostream>
using namespace std;
class Student
{
public:
Student();
Student(Student &student);
Student(string name, string surname);
~Student();
const string getName();
const string getSurname();
void setName(string name);
void setSurname(string surname);
void print();
private:
string name;
string surname;
};
Student.cpp
#include <iostream>
#include "Student.h"
using namespace std;
Student::Student()
{
}
Student::Student(string name, string surname)
{
this->name = name;
this->surname = surname;
}
Student::Student(Student &student) : name(student.getName()), surname(student.getSurname())
{
}
Student::~Student()
{
cout << "Object is destroyed" << endl;
}
const string Student::getName()
{
return name;
}
const string Student::getSurname()
{
return surname;
}
void Student::setName(string name)
{
name = this->name;
}
void Student::setSurname(string surname)
{
surname = this->surname;
}
void Student::print()
{
cout << "Student: " << name << " " << surname << endl;
}
Main.cpp
#include <iostream>
#include "Subject.h"
#include "Student.h"
using namespace std;
int main()
{
/*
* First three students should attend first Subject
* while other four the second Subject.
* Also note that only names matter and not surnames.
*/
Student stA("Michael", "Doe");
Student stB("Michael", "Doe");
Student stC("Thomas", "Doe");
Student stD("Nicholas", "Doe");
Student stE("Nicholas", "Doe");
Student stF("John", "Doe");
Student stG("John", "Doe");
Subject subjectA("C++", 3);
Subject subjectB("C", 4);
return 0;
}
1) Get an array of Students into your Subject object: you probably want to use vectors instead of arrays here:
in subject.h add
#include "Student.h"
public:
void addStudent(Student student);
private:
std::vector<Student> students_;
in subject.cpp add
void Subject::addStudent(Student student)
{
this->students_.push_back(student);
}
If you want to extract the student list somehow later, you need to write a function to access it (or make it public).
2) For finding duplicates, look here
Checking for duplicates in a vector
You have to pay attention: the Student objects are in your subject object, not the student names. You have to extract them first and e.g. put them in a vector.
Your task definition sais you should have an array of Students attribute of the Subject class, but i don't see this in your Subject class definition.
And maybe an add Student method and then iterate over the array.
I'm encountering an error that says:
Invalid operands to binary expression ('ostream' (aka 'basic_ostream') and 'void')
I understand there are some questions related to this error posted on StackOverflow but I need some help and explanations regarding this specific context on what this error means.
In the main() function, I create a student object called s1. The error happens in main() where I'm trying to get the results of his GPA using a method of the Student class called getResults(double gpa).
#include <iostream>
using namespace std;
class Human{
protected: string name;
protected: int age;
public: Human(){
name = "Unknown";
age = 5;
}
public:
Human(string name, int age){
this->name = name;
this->age = age;
}
string getName(){
return name;
}
int getAge(){
return age;
}
void setName(string name){
this->name = name;
}
void setAge(int age){
this->age = age;
}
};
class Student: public Human{
protected: string school;
protected: double gpa;
public:
Student(string name, int age, string school, double gpa) : Human(name, age){
this->school = school;
this->gpa = gpa;
}
double getGPA(){
return gpa;
}
string getSchool(){
return school;
}
void setGPA(double gpa){
this->gpa = gpa;
}
void setSchool(string school){
this->school = school;
}
void getResult(double gpa){
if (gpa < 3.0) {
cout << "You did well!";
} else {
cout << "Try harder next time";
}
}
};
int main() {
Student s1 ("John", 23, 'm', "University of Chicago", 3.4);
double s1GPA = s1.getGPA();
cout << s1.getResult(s1GPA) << endl;
return 0;
}
Currently, your getResults function has a void return type, which means it doesn't actually return anything. Because of this, do not try to cout the result of this function in your main.
Consider the following edit:
// Your result is printed within this function
s1.getResult(s1GPA);
// Print a new line if you wish
cout << endl;
Also, since your getResults doesn't really get anything, I'd suggest changing the name to something like printResults.
Note
Notice how in your getResult it doesn't return anything because it's a void. In this function, you're just outputting text to the console with cout:
// Notice that this function doesn't actually return anything
void getResult(double gpa){
if (gpa < 3.0) {
// Output this message to console
cout << "You did well!";
} else {
// Output this message to console
cout << "Try harder next time";
}
}
When you have the statement in your main, it's trying to cout nothing because getResult is a void:
cout << s1.getResult(s1GPA) << endl;
// ^^^^^^^^^^^^^^^^^^^
// This doesn't return anything for cout to output.
That is why you only need to call getResult instead of trying to cout it.
Whenever I try to make an object and call a function on it, it doesn't seem to work.
I have no idea why, since I don't seem to have errors too.
I have searched around on here regarding constructors and the toString-method, but haven't find anything that worked.
I have tried to edit (distinct) the members in the constructor members,
Tried to rewrite the toString method.
Tried to make local object (with no pointer).
But it doesn't return me the things in the object that I created when calling the constructor.
Where does the problem situate in this problem?
Here is my code:
.h file:
#pragma once
#include "stdafx.h"
#include <string>
#include <sstream>
#include <iostream>
using namespace std;
class Store{
private:
int id;
string name;
string adress;
string telephone;
string btwNumber;
public:
int getId();
void setId(int);
string getName();
void setName(string);
string getAdress();
void setAdress(string);
string getTelephone();
void setTelephone(string);
string getBtwNumber();
void setBtwNumber(std::string);
string toString();
Store(int, string, string , string, string);
};
.cpp file:
// Store.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include "Store.h"
Store::Store(int idnum, string nameS, string adreS, string telephonE, string btwnummeR){
idnum = id;
nameS = name;
adreS = adress;
telephonE = telephone;
btwnummeR = btwNumber;
}
int Store::getId()
{
return id;
}
void Store::setId(int id){
this->id = id;
}
string Store::getName(){
return naam;
}
void Store::setName(string name){
this->naam = naam;
}
string Store::getTelephone(){
return telephone;
}
void Store:setTelephone(string telephone){
this->telephone = telephone;
}
string Store::getBtwNumber()
{
return btwNumber;
}
void Store::setBtwNumber(string btwNumber){
btwNumber = btwNumber;
}
string Store::getAdress(){
return adress;
}
void Store::setAdress(string adress){
this->adress = adress;
}
string Store::toString(){
stringstream s;
s << "Id: " << id << endl;
s << "Naam: " << name << endl;
s << "Adres: " << adress << endl;
s << "Telefoonnummer: " << telephone << endl;
s << "BTWnummer: " << btwNumber << endl;
return s.str();
}
int _tmain(int argc, _TCHAR* argv[])
{
Store *test = new Store (4, "Test", "test", "test", "test");
test->toString();
system("Pause");
return 0;
}
Your constructor is inversed: you are assigning member variables to constructor arguments and not vice versa.
nameS = name;
Should be
name = nameS;
And so on
The method toString does work, but it won't magically decide to output its return value to screen. You'll have to do it yourself:
std::cout << test->toString() << std::endl;
You'll need to add #include <iostream> on top of your cpp file.