The reason is only one sentence: Determine the namespace of an object to help avoid name conflicts in your program, especially in a large program, this decision is also important.
A typical standard C namespace comparative statement such as: use namespace std; (pay attention to the subunies behind, can not be omitted)
But even use "Using Namespace Std;", you still can't avoid name conflicts. Because you bring all the names in the STD name in the entire program, it is generally not recommended to use "useing namespace std;", if you really need it, it is recommended that you use some objects when you use it. Format:
STD: Object Name, such as: std :: cout, std :: cin, etc.
