How do I this program with constructor?

Question

1.00/5 (1 vote)

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#include<iostream>
using namespace std;
class Person
{
        private:
		char name[20], work[30];
        int age;
        public:
		void input();
        void display();
                        
                
};
void Person::input()
{
        cout<<"Enter Name:";
        cin>>name;
        cout<<"Enter Age:";
        cin>>age;
        cout<<"Enter Work:";
        cin>>work;
}
void Person::display()
{
        cout<<"\nName:"<<name;
        cout<<"\nAge:"<<age;
        cout<<"\nWork:"<<work;
        
}
int main()
{
        Person p;
        p.input();
        p.display();
}

What I have tried:

#include<iostream>
using namespace std;
class Person 
{        
  private:          
    string name;  
    string work; 
    int age;      
    Person(string n, string w, int a); 
};


Person::Person(string n, string w, int a) 
{
	    cout<<"Enter Name:";
        cin>>n;
        cout<<"Enter Age:";
        cin>>a;
        cout<<"Enter Work:";
        cin>>w;
  		name=n;
  		work=w;
  		age=a;
}

int main() 
{
  
  Person p
  

  cout << p.name << " " << p.work << " " << p.age << "\n";
  
  return 0;
}

Posted 2-Jun-21 8:16am

User 15142741

Updated 4-Jun-21 7:58am

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6 solutions

Solution 1

Don't do it like that: the Person class should know nothing about the environment in which it is running, so it should never assume that the console will be available. Hence, it should never try to get information directly from the user, but get the name, age, and job title passed to it as constructor parameters when the new instance is created.

The main function can prompt the user and get the responses, store them, and pass them to the Person class when it builds it.

That way, you can reuse the same class to hold a collection of people read from a file or a database for example, or from textboxes in a windows or web based app without any changes to it.

Posted 2-Jun-21 9:12am

OriginalGriff

Comments

[no name] 2-Jun-21 15:29pm

that is, what should I do??

OriginalGriff 2-Jun-21 16:00pm

Read what I said, read your course notes, and then start coding?

[no name] 2-Jun-21 16:23pm

my english is not good and google translate does not help much

OriginalGriff 2-Jun-21 16:25pm

Which bits are giving you problems?

[no name] 2-Jun-21 16:26pm

"The main function can prompt the user and get the responses, store them, and pass them to the Person class when it builds it."

OriginalGriff 2-Jun-21 16:33pm

OK - so you know how to read data from the user, yes? Your existing code does that, just in the wrong place.
So move the input code into the main function and store the results in local variables.

Then write a Person constructor that accepts three parameters - your course notes will show you ha=ow to do that.
The constructor copies the parameter data to the class instance.

Then just call the constructor from main when you create the instance and pass your local data to it.

Make sense?

[no name] 2-Jun-21 17:01pm

#include<iostream>
using namespace std;
class Person
{
private:
string name;
string work;
int age;
Person(string n, string w, int a);
};

Person::Person(string n, string w, int a)
{

name=n;
work=w;
age=a;
}

int main()
{
Person p;
char n, w;
int a;

cout<<"Enter Name:";
cin>>n;
cout<<"Enter Age:";
cin>>a;
cout<<"Enter Work:";
cin>>w;

cout << p.name << " " << p.work << " " << p.age << "\n";

return 0;
}

OriginalGriff 3-Jun-21 4:07am

Errr ... no.
Read what I said, read your course notes.

I'm not writing this for you!

[no name] 3-Jun-21 4:19am

i don't want you to write this, but i don't understand how to use the constructor and why to use this....

OriginalGriff 3-Jun-21 4:28am

Read your course notes: at the moment the code you are showing us is guesswork: you aren't thinking about what you have been told and trying to apply it, you are just hammering out code and hoping it will work.

That's not a viable development strategy: this is stuff you are going to use on every single class you create from now on, so it;'s stuff you have to understand - so just looking at an example I could give you isn't going to help any more than the ones your teacher did!

Seriously, read the notes, and think about them - you need to know this stuff to progress!

[no name] 4-Jun-21 6:02am

is this correct???

OriginalGriff 4-Jun-21 6:03am

Why are you asking a question, if you then ignore everything you are told?

[no name] 4-Jun-21 6:06am

below I have a solution I made with the notes is not correct ??

Solution 2

a normal pattern for this is a factory function which does your person code with asking the user for input BEFORE creating the object and best practice is that some checking like age over 0 and name not empty. If no valid person can be created it returns NULL which handles the external code.

Posted 2-Jun-21 10:43am

KarstenK

Solution 6

#include<iostream>
using namespace std;
/*me thn xrhsh constructor emfanizw to onoma thn douleia kai thn hlikia*/

class Person
{
	private:
  	string name;
  	string work;
  	int age;
	public:
  	Person(string  name, string work, int age) : name(name), work(work), age(age)
 	 {
  		}
  	string get_name() { return name; }
  	string get_work() { return work; }
  	int get_age() { return age; }
};


int main()
{
  	string name, work;
  	int age;
  
  	cout<<"Enter Name:";
	cin >> name;
	
	cout<<"Enter work:";
	cin >> work;
	

	cout<<"Enter Age:";
	cin >> age;

	Person p(name, work, age);

    cout <<"\n"<< "name: "<< p.get_name()<<"\n"<< "work: "<< p.get_work()<<"\n"<< "age: "<< p.get_age()<< endl;
}

thanks all for your help!!!!!

Posted 4-Jun-21 7:58am

User 15142741

Solution 3

#include<iostream>
using namespace std;
class Person
{
        private:
		char name[20], work[30];
        int age;
        public:
		Person();
		~Person();
		void getname();
		void getage();
		void getwork();
                        
                
};
Person::Person()
{
	cout<<"Enter Name:";
	gets(name);
	
	cout<<"Enter Work:";
	gets(work);
	
	do{
	cout<<"Enter Age:";
	cin>>age;
	}while(age<1);
	


}
Person::~Person()
{
	
}
void Person::getname()
{
	puts(name);
}
void Person::getwork()
{
	puts(work);
}
void Person::getage()
{
	cout<<age;
}


int main()
{
	
	Person p;
	
	cout<<"\nName:";
	p.getname();
	
	cout<<"\nWork:";
	p.getwork();
	
	cout<<"\nAge:";
	p.getage();
	

	return 0;
}

Posted 4-Jun-21 0:01am

User 15142741

Comments

Dave Kreskowiak 4-Jun-21 13:51pm

Wrong again. DO NOT use cin, cout, gets, or puts in ANY of your Person class code.

The Person class should only be concerned with holding and manipulating the data of a Person. It should NEVER have anything to do with getting that data from the user, nor outputting that data to the console.

[no name] 4-Jun-21 13:56pm

#include<iostream>
using namespace std;
/*me thn xrhsh constructor emfanizw to onoma thn douleia kai thn hlikia*/

class Person
{
private:
string name;
string work;
int age;
public:
Person(string name, string work, int age) : name(name), work(work), age(age)
{
}
string get_name() { return name; }
string get_work() { return work; }
int get_age() { return age; }
};

int main()
{
string name, work;
int age;

cout<<"Enter Name:";
cin >> name;

cout<<"Enter work:";
cin >> work;

cout<<"Enter Age:";
cin >> age;

Person p(name, work, age);

cout <<"\n"<< "name: "<< p.get_name()<<"\n"<< "work: "<< p.get_work()<<"\n"<< "age: "<< p.get_age()<< endl;
}

now work!!!

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CPallini · Accepted Answer · 2021-06-04T00:33:00

You look a bit confused.
As already suggested, you should avoid I/O calls in your class, on the contrary, the main function should collect input from the user, call the object constructor and produce the output based on the object properties (publicly exposed as methods).
Try, for instance

C++

#include<iostream>
using namespace std;


class Person
{
  string name;
  string job;
  int age;
public:
  Person(string  name, string job, int age) : name{name}, job{job}, age{age}
  {
  }
  string get_name() { return name; }
  string get_job() { return job; }
  int get_age() { return age; }
};


int main()
{
  string name, job;
  int age;

  cout << "plaese enter name, job and age: \n";

  cin >> name >> job >> age;

  Person p{ name, job, age };

  cout << "name = " << p.get_name() << ", job = " << p.get_job() << ", age = " << p.get_age() << endl;
}

Stefan_Lang · Accepted Answer · 2021-06-04T06:46:00

Since you are just beginning to learn, I will try to point you only to the steps you need to do first:

1. You asked for a solution that uses a constructor. So write a constructor. In the comments you already offered one version with a working constructor: it had three function arguments and assigned them to the internal data members. That's right, keep this. CPallini also offered one. It uses a different syntax but does essentially the same thing. If you want to learn about this syntax, google for "c++ member initializer list"

2. Next, to use this constructor, you must first determine the values for the constructor arguments. As the others already pointed out, define variables for these arguments within the main function, then read the values like you did in your original input function and store the inputs into your variables.

3. After you have read all the variables, you can call the constructor. Note that you can not define a variable of type person before you have the arguments needed for the constructor! Since you seem to have trouble about constructor syntax, to call a constructor with arguments, you have to list the arguments in brackets after the variable name, e. g.:
Person p(name, job, age);
instead of just:
Person p;

4. Last you can call the display method, but you already did that.

There are a number of things to improve this code, but for now just make it work as described here.

If you like, you can think on OriginalGriffs comment that the class Person should not know about the console - this does not only refer to the input, but also to the display function! So, to take your task one step further: what would it take to move the console I/O entirely out of the class Person?

How do I this program with constructor?

6 solutions

Solution 1

Solution 4

Solution 5

Solution 2

Solution 6

Solution 3

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