Question

This code returns me an error whenever I try to run this code. Can some one please help me.

struct m
{
    virtual int s( )
    { 
        return 1;
    }
};

struct n : public m
{
    int s( )
    { 
        return 2;
    }
};

int o( )
{
    n* p=new m;
    m* q=dynamic_cast<p>;
    return q->s( );
}

Answer 1

These C++ cast operators should be used as

dynamic_cast<newType>(variable)

In your case,

m* q = dynamic_cast<m*>(p); 

BTW, are you confusing the role of m and n? n* p = new m is a syntax error because a base class instance cannot be implicitly converted to a derived class instance. In fact, base → derived is the situation where you actually need dynamic_cast, not the other way around (no casting is needed).

Also, consider giving meaningful names to objects.