Csharp/C Sharp/Data Types/Nulllable

Declare a nullable type by adding the ? type modifier in a value type declaration.

<source lang="csharp"> using System; public class MainClass {

   double? variable1 = null;
   static void Main() {
       int? variablea = null;
       Console.WriteLine(variablea.HasValue); // false
       int variableb = variablea ?? 5;
       Console.WriteLine(variableb); // 5
   }

}

</source>

Nullable bool Types

<source lang="csharp"> using System; using System.Collections.Generic; using System.Text; class DatabaseReader {

   // Nullable data field.
   public int? numbericValue;
   public bool? boolValue = true;
   // Note the nullable return type. 
   public int? GetIntFromDatabase() { return numbericValue; }
   // Note the nullable return type. 
   public bool? GetBoolFromDatabase() { return boolValue; }

} class Program {

   static void Main(string[] args) {
       DatabaseReader dr = new DatabaseReader();
       int? i = dr.GetIntFromDatabase();
       if (i.HasValue)
           Console.WriteLine("Value of "i" is: {0}", i);
       else
           Console.WriteLine("Value of "i" is undefined.");
       // Get bool from "database".
       bool? b = dr.GetBoolFromDatabase();
       if (b != null)
           Console.WriteLine("Value of "b" is: {0}", b);
       else
           Console.WriteLine("Value of "b" is undefined.");
       // If the value from GetIntFromDatabase() is null, 
       // assign local variable to 100.
       int? myData = dr.GetIntFromDatabase() ?? 100;
       Console.WriteLine("Value of myData: {0}", myData);
   }

}

</source>

Nullable int Types

<source lang="csharp"> using System; using System.Collections.Generic; using System.Text; class DatabaseReader {

   // Nullable data field.
   public int? numbericValue;
   public bool? boolValue = true;
   // Note the nullable return type. 
   public int? GetIntFromDatabase() { return numbericValue; }
   // Note the nullable return type. 
   public bool? GetBoolFromDatabase() { return boolValue; }

} class Program {

   static void Main(string[] args) {
       DatabaseReader dr = new DatabaseReader();
       int? i = dr.GetIntFromDatabase();
       if (i.HasValue)
           Console.WriteLine("Value of "i" is: {0}", i);
       else
           Console.WriteLine("Value of "i" is undefined.");
       // Get bool from "database".
       bool? b = dr.GetBoolFromDatabase();
       if (b != null)
           Console.WriteLine("Value of "b" is: {0}", b);
       else
           Console.WriteLine("Value of "b" is undefined.");
       // If the value from GetIntFromDatabase() is null, 
       // assign local variable to 100.
       int? myData = dr.GetIntFromDatabase() ?? 100;
       Console.WriteLine("Value of myData: {0}", myData);
   }

}

</source>

Nullable variable

<source lang="csharp">

using System; using System.Collections.Generic; using System.Text; public class Vector {

   public double? R = null;
   public double? Theta = null;
   public double? ThetaRadians {
       get {
           return (Theta * Math.PI / 180.0);
       }
   }
   public Vector(double? r, double? theta) {
       if (r < 0) {
           r = -r;
           theta += 180;
       }
       theta = theta % 360;
       R = r;
       Theta = theta;
   }
   public static Vector operator +(Vector op1, Vector op2) {
       try {
           double newX = op1.R.Value * Math.Sin(op1.ThetaRadians.Value)
              + op2.R.Value * Math.Sin(op2.ThetaRadians.Value);
           double newY = op1.R.Value * Math.Cos(op1.ThetaRadians.Value)
              + op2.R.Value * Math.Cos(op2.ThetaRadians.Value);
           double newR = Math.Sqrt(newX * newX + newY * newY);
           double newTheta = Math.Atan2(newX, newY) * 180.0 / Math.PI;
           return new Vector(newR, newTheta);
       } catch {
           return new Vector(null, null);
       }
   }
   public static Vector operator -(Vector op1) {
       return new Vector(-op1.R, op1.Theta);
   }
   public static Vector operator -(Vector op1, Vector op2) {
       return op1 + (-op2);
   }
   public override string ToString() {
       string rString = R.HasValue ? R.ToString() : "null";
       string thetaString = Theta.HasValue ? Theta.ToString() : "null";
       return string.Format("({0}, {1})", rString, thetaString);
   }

} class Program {

   public static void Main(string[] args) {
       Vector v1 = GetVector("vector1");
       Vector v2 = GetVector("vector1");
       Console.WriteLine("{0} + {1} = {2}", v1, v2, v1 + v2);
       Console.WriteLine("{0} - {1} = {2}", v1, v2, v1 - v2);
       Console.ReadKey();
   }
   public static Vector GetVector(string name) {
       Console.WriteLine("Input {0} magnitude:", name);
       double? r = GetNullableDouble();
       Console.WriteLine("Input {0} angle (in degrees):", name);
       double? theta = GetNullableDouble();
       return new Vector(r, theta);
   }
   public static double? GetNullableDouble() {
       double? result;
       string userInput = Console.ReadLine();
       try {
           result = double.Parse(userInput);
       } catch {
           result = null;
       }
       return result;
   }

}

</source>

Nulllable HasValue

<source lang="csharp">

using System; using System.Collections.Generic; using System.Text;

public class MyTest {

   public static void NullableTest(Nullable<int> intVal1, int intVal2) {
       if (intVal1.HasValue == true)
           Console.WriteLine(intVal1);
       else
           Console.WriteLine("Value1 is NULL");
       if (intVal2 > 0)
           Console.WriteLine(intVal2);
       else
           Console.WriteLine("Value2 is Null?");
   }

}

      </source>