Using namespace std

Using namespace std

 

STD is a namespace ..
Different namespaces can have the same class name defined ..
Using namespace STD;
Indicates that the following program uses STD. If this statement is not used, use STD: string (string is defined in the STD space.
It can also be defined in the global space, as long as the namespace is different ..)..
Otherwise, the default namespace contains STD. Instead of STD :.
It is part of the new C ++ standard and solves the name conflict problem when many people compile large programs.
For example, if both A and B have a name named Zhang San, you must first name the namespace of Class A if you want to use Zhang San of Class ), then, you can use all the commands of James to meet your expectation.

If you use # include <iostream. h>, you do not need to write this statement (the old standard ). But if you use
# Include <iostream> must be written.