Exceptions and Defensive Coding

Null Checks

A null check chooses a fallback before using a missing nullable value.

Null Checks

NullChecks.cs 
using System;

class Program
{
    static string DisplayScore(int? score)
    {
        if (!score.HasValue)
        {
            return "missing";
        }

        return "score:" + score.Value;
    }

    static void Main()
    {
        int? score = ;
        string display = DisplayScore(score);

        Console.WriteLine($"hasScore={score.HasValue}");
        Console.WriteLine($"display={display}");
    }
}

using System;

class Program
{
    static string DisplayScore(int? score)
    {
        if (!score.HasValue)
        {
            return "missing";
        }

        return "score:" + score.Value;
    }

    static void Main()
    {
        int? score = ;
        string display = DisplayScore(score);

        Console.WriteLine($"hasScore={score.HasValue}");
        Console.WriteLine($"display={display}");
    }
}

using System;

class Program
{
    static string DisplayScore(int? score)
    {
        if (!score.HasValue)
        {
            return "missing";
        }

        return "score:" + score.Value;
    }

    static void Main()
    {
        int? score = ;
        string display = DisplayScore(score);

        Console.WriteLine($"hasScore={score.HasValue}");
        Console.WriteLine($"display={display}");
    }
}
null check A null check protects code before reading from a value that might be missing.