# access specifier in c#

In C#, access specifiers are keywords used to define the scope and visibility of classes, methods, properties, and other members within a program. There are four access specifiers in C#:

1. `public`: Public members are accessible from anywhere within the program, both inside and outside the defining class.
    
2. `private`: Private members are accessible only within the defining class. They cannot be accessed from outside the class, not even by derived classes.
    
3. `protected`: Protected members are accessible within the defining class and by derived classes. They cannot be accessed from outside the class hierarchy.
    
4. `internal`: Internal members are accessible only within the assembly (a DLL or EXE) in which they are defined. They cannot be accessed from outside the assembly.
    

Here's an example to illustrate the usage of access specifiers in C#:

```csharp
csharpCopy codeclass Person
{
    public string Name; // Public member
    private int Age; // Private member
    protected string Address; // Protected member
    internal bool IsMarried; // Internal member

    public void Display()
    {
        Console.WriteLine($"Name: {Name}, Age: {Age}, Address: {Address}, IsMarried: {IsMarried}");
    }
}

class Employee : Person
{
    public void UpdateAddress(string newAddress)
    {
        Address = newAddress; // Accessing protected member of the base class
    }
}

class Program
{
    static void Main(string[] args)
    {
        Person p = new Person();
        p.Name = "John Doe"; // Accessing public member
        // p.Age = 30; // This will result in a compile-time error since Age is a private member
        // p.Address = "123 Main St."; // This will result in a compile-time error since Address is a protected member
        p.IsMarried = true; // Accessing internal member

        Employee e = new Employee();
        e.Name = "Jane Smith"; // Accessing public member of base class
        // e.Age = 35; // This will result in a compile-time error since Age is a private member of the base class
        e.UpdateAddress("456 Second Ave."); // Accessing protected member of base class through derived class
        e.IsMarried = false; // Accessing internal member of base class through derived class

        p.Display();
        e.Display();
    }
}
```

In this example, we have a class `Person` with four members that use different access specifiers. The `Name` member is public, so it can be accessed from anywhere. The `Age` member is private, so it can only be accessed within the `Person` class. The `Address` member is protected, so it can be accessed within the `Person` class and by derived classes such as `Employee`. The `IsMarried` member is internal, so it can be accessed only within the same assembly.

In the `Main` method, we create an instance of `Person` and `Employee` and access their members using the appropriate access specifiers. We can see that public members can be accessed from anywhere, private members cannot be accessed outside the defining class, protected members can be accessed within the class hierarchy, and internal members can be accessed within the same assembly.