Exceptions and Defensive Coding

Guard Clauses

A guard clause handles invalid input before the main work continues.

Guard Clauses

GuardClauses.cs 
using System;

class Program
{
    static int ShippingCost(int quantity)
    {
        if (quantity <= 0)
        {
            return 0;
        }

        return 5 + quantity;
    }

    static void Main()
    {
        int quantity = ;
        int cost = ShippingCost(quantity);

        Console.WriteLine($"quantity={quantity}");
        Console.WriteLine($"cost={cost}");
    }
}

using System;

class Program
{
    static int ShippingCost(int quantity)
    {
        if (quantity <= 0)
        {
            return 0;
        }

        return 5 + quantity;
    }

    static void Main()
    {
        int quantity = ;
        int cost = ShippingCost(quantity);

        Console.WriteLine($"quantity={quantity}");
        Console.WriteLine($"cost={cost}");
    }
}

using System;

class Program
{
    static int ShippingCost(int quantity)
    {
        if (quantity <= 0)
        {
            return 0;
        }

        return 5 + quantity;
    }

    static void Main()
    {
        int quantity = ;
        int cost = ShippingCost(quantity);

        Console.WriteLine($"quantity={quantity}");
        Console.WriteLine($"cost={cost}");
    }
}
guard clause A guard clause returns early when a value should not continue through a method.