a pointer to a function question..

Yes.

Originally Posted by transgalactic2

why only ptr=add;

Code:

why not ptr=add(int x,int y);  //add is a function we cant hide its signature 
                                            //what if there were two add function but with different signatures
                                            //in such case this line will create an error

??

Because that is a declaration, not an assignment.
It's also possible to create several functions with different parameter lists (with the same name). It's called overloading and is available in C++, but not C.

Well it isn't a declaration either (just to be clear). The code is a mistake if we want to call it anything. The reason you can't do that is because it isn't a valid C statement, and that will stop the compiler every time.