Namespace

Namespaces are used to organize code into logical groups and to prevent name collisions that can occur especially when your code base includes multiple libraries. We can have namespace inside namespace(Sub-namespace). In order to declare namespace we need to use namespace keyword and we need to give name for that.

Syntax
namespace namespaceName{
    //Sub-namespaces , classes
}

In order to access members of a class which is present inside difference namespace. We need to first call the outer most namespace then we need to call sub namespaces then we need to call class then only we can access members of that particular class. We'll see this with code example below

CODE

EG 1 . Creating a namespace with a class and a Sub-namespace.

//Either we can refer namespace here or we can each time call individual namespaces and access its member(Explained clearly in CODE EXPLANATION).
using NewlyCreatedNamespace;
using NewlyCreatedNamespace.subNamespace1.space;

namespace NewlyCreatedNamespace {
    public static class basicMath {
        public static double Deg2Rad(double degree) {
            return degree * Math.PI / 180;
        }
        public static double Rad2Deg(double radian) {
            return radian * 180 / Math.PI;
        }
    }
    namespace subNamespace1 {
        namespace space {
            public class rectangle {
                public double length, width, height;
                public double Area() {
                    return length * width;
                }
                public double Perimeter() {
                    return 2 * (length + width);
                }
                public double Volume() {
                    return Area() * height;
                }
            }
        }
    }
}

namespace ProjectName {
    internal class Program {
        static void Main() {
            //We need to give entire directory of namespaces then only we can access class and its members.
            NewlyCreatedNamespace.basicMath.Deg2Rad(30);
            NewlyCreatedNamespace.subNamespace1.space.rectangle wall = new NewlyCreatedNamespace.subNamespace1.space.rectangle();
        }
    }
}

CODE EXPLANATION
In the above code, we created namespace called NewlyCreatedNamespace . Inside that we created 1 class called basicMath and 1 sub-namespace called subNamespace1. That subNamespace1 is having one more sub-namespace called space. Inside that we created 1 class called rectangle. In order to access the Deg2Rad method present inside basicMath, first we need to call NewlyCreatedNamespace then basicMath class then only we can access Deg2Rad method. If we want to access rectangle class, we need to first call NewlyCreatedNamespace then subNamespace1 then space namespace then only we can access rectangle class. Apart from these other functions are same as that of what we studied before.

Here each time calling individual namespace is not required, we can use using keyword to refer namespaces.
using NewlyCreatedNamespace;
using NewlyCreatedNamespace.subNamespace1.space;
once we declare above codes in the starting, we no need to each time call namespaces we can directly access the class present inside it. If we want to access class directly we can refer namespace by using keyword or we can each time call individual namespace then access classes present inside it.


Where to use Namespace?
The only use of namespace is to organize code elements into a group. Namespace also solves the problem of naming conflict. Two or more classes when put into different namespaces can have same name. Namespaces are not mandatory in a C# program, but they do play an important role in writing cleaner codes and managing larger projects.

Exercises
1. Create a namespace with 5 sub-namespaces and write mixture of static and non static classes inside each sub-namespace. Try to invoke all classes inside main method.

(Click Here, For more exercises)