identifier "poly1" is undefined error

myoni (43)
why I'm getting error message : identifier "poly1" is undefined

in line: cout<<(poly1==poly2);
why and how to repair it ?
this is my code:

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#include <iostream>
using namespace std;

class closedPolynom
{..};

class Triangle : public closedPolynom
{..};

class Rectangle : public closedPolynom
{..};

void main()
{
	int num;
	cin>>num;
	if (num==3)
		Triangle poly1(num);
	else if (num==4)
		Rectangle poly1(num);
	else
		closedPolynom poly1(num);

	cin>>num;
	if (num==3)
		Triangle poly2(num);
	else if (num==4)
		Rectangle poly2(num);
	else
		closedPolynom poly2(num);

	cout<<endl;
	cout<<(poly1==poly2);
}
vlad from moscow (6539)
The problem is that if and else statements have their own block scopes. So after executing of if-else was finished defined variables were deleted.

To make it clear the following two statements are equivalent


if (num==3) Triangle poly2(num);

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if (num==3)
{
	Triangle poly2(num);
}
Last edited on
myoni (43)
so, what can I do, if I want to declare on appropiate class type according to user input ?
Peter87 (11254)
This
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if (num==3)
	Triangle poly1(num);
else if (num==4)
	Rectangle poly1(num);
else
	closedPolynom poly1(num);
is the same as this
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if (num==3)
{
	Triangle poly1(num);
}
else if (num==4)
{
	Rectangle poly1(num);
}
else
{
	closedPolynom poly1(num);
}

As you see. poly1 will go out of scope on the line after it was created.

If you want to do something like this you should use a pointer to the base class and create the object dynamically.
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closedPolynom* poly1 = 0;
if (num==3)
	poly1 = new Triangle(num);
else if (num==4)
	poly1 = new Rectangle(num);
else
	poly1 = new closedPolynom(num);

Don't forget to delete the object when you no longer need it.delete poly1;
Do the same with poly2.
myoni (43)
thanx
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