How to declare and initialize constant strings in C#?

To declare a constant string in C#, use the const keyword. Constants are immutable values that are set at compile-time and cannot be changed during program execution. Once initialized, attempting to modify a constant will result in a compile-time error.

Syntax

Following is the syntax for declaring and initializing a constant string −

const string constantName = "value";

Constants must be initialized at the time of declaration and the value must be a compile-time constant expression.

Key Rules for Constants

• Constants must be initialized at declaration − you cannot declare and assign later.

• The value must be a compile-time constant − literals, null, or expressions of constants.

• Constants are implicitly static and shared across all instances of the class.

• Attempting to modify a constant after declaration results in a compile-time error.

Example

using System;

class Demo {
   const string one = "Amit";

   static void Main() {
      // displaying first constant string
      Console.WriteLine(one);

      const string two = "Tom";
      const string three = "Steve";

      // compile-time error if uncommented
      // one = "David";

      Console.WriteLine(two);
      Console.WriteLine(three);
   }
}

The output of the above code is −

Amit
Tom
Steve

Constants vs Readonly Variables

Using Multiple Constants

using System;

class AppConstants {
   public const string APP_NAME = "My Application";
   public const string VERSION = "1.0.0";
   public const string COMPANY = "Tech Corp";
   
   static void Main() {
      Console.WriteLine("Application: " + APP_NAME);
      Console.WriteLine("Version: " + VERSION);
      Console.WriteLine("Company: " + COMPANY);
      
      // Demonstrating constants are accessible without creating instance
      Console.WriteLine("Full Info: " + APP_NAME + " v" + VERSION + " by " + COMPANY);
   }
}

The output of the above code is −

Application: My Application
Version: 1.0.0
Company: Tech Corp
Full Info: My Application v1.0.0 by Tech Corp

Conclusion

Constant strings in C# are declared using the const keyword and must be initialized with compile-time constant values. They are immutable, implicitly static, and provide a way to define unchanging string values that are shared across all instances of a class.