What's wrong in this program.plz tell me

[Alam]

The purpose of writing using namespace std; is that

The program will know to look in the std library to find the object. Namespace std contains all the classes, objects and functions of the standard C++ library.

[MUHAMMAD12]

JAZAKALLAH alam.so after writing using name space std we do not have to write other directives like <math>,<string> etc.?am i right?

[z05DSL3A]

http://www.cplusplus.com/doc/tutorial/namespaces/

[Catfish2]

And a rusty nail is good enough for digging red-hot shrapnel out of your arm.

Dev-C++ is good enough for C++03.

[Chervil]

The real point is not what anyone chooses to use.
It is what they choose to recommend.

The two may not be the same.