Pls comment for further improvements...

[MaBunny]

Ive written a stack class.Heres the code: http://paste.debian.net/417593/
And main.cpp: http://paste.debian.net/417592/

I hav received various suggestions from Moschops and others.Pls help me in giving more suggestions guys.Ill use it in a program for a Mathematical parserr.

[Moschops]

You are throwing and catching exceptions within the same function, just to output to cerr. Why bother?

Replace throw 3; with std::cerr<< "Tried to delete top of the Stack,which is a nullptr !!!\n"; and similarly for others.

[MaBunny]

So,i shouldnt include the nested class into the Stack class,ok.
Thnx Moschops!

[MaBunny]

Heres the errors corrected: http://paste.debian.net/417617/

[Moschops]

You are throwing and catching exceptions within the same function, just to output to cerr. Why bother?

Replace throw "Tried to delete top of the Stack,which is a nullptr !!!\n"; with std::cerr<< "Tried to delete top of the Stack,which is a nullptr !!!\n"; and similarly for others.

[Thomas1965]

Normally you throw exceptions in the code that has to report an error it can't handle. You catch an exception when you can deal with the error.

Stack :: ~Stack()
Why would you want to throw an exception here. An empty stack is not an error.
void Stack :: pop()
Trying to pop an empty stack is definitely an error and should be reported to the caller.
void Stack :: push(int &a)
How can yo actually get an stack overflow? If there is not enough memory you will get an bad_alloc exception from new

node *RET_topnode()
    {
	return top;
    }

Why don't you return the value instead of a node?