CODEWITHSUNDEEP
c++
Slazer
Slazer

Reputation: 4990

Printing string depending on user input

The switch statement in this code does not work. It should define (global) variable x to be instance of class A if the user press 1 and of class B if the user press 2. I would like to print A if user presses 1 and print B if she presses 2. I want to use the "x.print()" statement, where x is either class A or class B, depending on the input.

#include <iostream>
using namespace std;

class A{
public:
    void print(){cout<<"A";}
};

class B{
public:
    void print(){cout<<"B";}
};

int main() {
    int choice;
    cout<<"Press 1 to print A\nPress 2 to print B\n";
    cin>>choice;

    //I know the following does not work, it's just to show what I want to do
    switch (choice){
    case 1: A x;
            break;
    case 2: B x;
            break;
    }

    x.print();
    return 0;
}

Upvotes: 0

Views: 131

Answers (4)

Amadeus
Amadeus

Reputation: 10655

Try this code. It use polimorphism to get what do you want:

#include <iostream>
using namespace std;

class Base {
public:
  virtual void print() = 0;
};

class A : public Base{
public:
    void print(){cout<<"A";}
};

class B : public Base{
public:
    void print(){cout<<"B";}
};

int main() {
    int choice;
    cout<<"Press 1 to print A\nPress 2 to print B\n";
    cin>>choice;

    Base *x = NULL;

    //I know the following does not work, it's just to show what I want to do
    switch (choice){
    case 1: x = new A();
            break;
    case 2: x = new B();
            break;
    }

    x->print();

    delete x;
    return 0;
}

Upvotes: 1

Saksham
Saksham

Reputation: 9380

You can modify your answer as

#include <iostream>
using namespace std;
class super
{
public:
    virtual void print() = 0;
};
class A: public super{
public:
    void print(){cout<<"A";}
};

class B: public super{
public:
    void print(){cout<<"B";}
};

int main() {
    int choice;
    cout<<"Press 1 to print A\nPress 2 to print B\n";
    cin>>choice;

    super* x;
    switch (choice){
    case 1: x = new A() ;
            break;
    case 2: x = new B();
            break;
    }

    x->print();
    return 0;
}

In this, we are creating an interface which is implemented by both class A and class B. And then using runtime polymorphism, we are creating the object of required class.

Upvotes: 1

rukamir
rukamir

Reputation: 46

It seems like what you are trying to do is create similar object based on conditions. For this I would suggest inheritance.

class Base{
public:
        virtual void print()=0;
};

class A : public Base{
public:
        void print(){cout << "This is class A\n";}
}

so main would look like:

Base* x = NULL;
switch (choice){
    case 1: x = new A();
            break;
    case 2: x = new B();
            break;
    }

This is what it seems like you are trying to do.

Upvotes: 1

Timo Geusch
Timo Geusch

Reputation: 24351

You're not going into detail as to what is actually broken but from a quick glance at your code, there is a bunch of problems in there:

  • Both "x" objects are scoped by the switch statement and don't exist by the time the code execution gets to x.print().
  • The classes A and B are completely unrelated, thus the compiler will not be able to figure what you mean by x.print();. You have to make sure the classes are related, either by deriving one from the other or by giving both classes a common ancestor
  • The print functions in the various classes aren't virtual so you can't get polymorphic behaviour anyway

Upvotes: 1

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