C# program applies bonus points

using System;
 
class BonusScore
{
    static void Main()
    {
        Console.WriteLine("Please enter integer between 1 and 9: ");
        int a = int.Parse(Console.ReadLine());
 
        if (a == 1 || a == 2 || a == 3)
        {
            Console.WriteLine("The BONUS score is: {0}", (a * 10));
        }
        else if (a == 4 || a == 5 || a == 6)
        {
            Console.WriteLine("The BONUS score is: {0}", (a * 100));
        }
        else if (a == 7 || a == 8 || a == 9)
        {
            Console.WriteLine("The BONUS score is: {0}", (a * 1000));
        }
        else
        {
            Console.WriteLine("Invalid score!");
        }
    }
}

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using System;
 
class BonusNumber
{
    static void Main()
    {
        Console.WriteLine("Please write a number between 1 and 9: ");
        int a = int.Parse(Console.ReadLine());
 
        switch (a)
        {
            case 1:
            case 2:
            case 3:
                Console.WriteLine("The BONUS score is: " + (a * 10));
                break;
            case 4:
            case 5:
            case 6:
                Console.WriteLine("The BONUS score is: " + (a * 100));
                break;
            case 7:
            case 8:
            case 9:
                Console.WriteLine("The BONUS score is: " + (a*1000));
                break;
            default:
                Console.WriteLine("Invalid Score!");
                break;
 
        }
    }
}

using System;
 
class BonusNumber
{
    static void Main()
    {
        Console.WriteLine("Please write a number between 1 and 9: ");
        int a = int.Parse(Console.ReadLine());
 
        switch (a)
        {
            case 1:
            case 2:
            case 3:
                Console.WriteLine("The BONUS score is: " + (a * 10));
                break;
            case 4:
            case 5:
            case 6:
                Console.WriteLine("The BONUS score is: " + (a * 100));
                break;
            case 7:
            case 8:
            case 9:
                Console.WriteLine("The BONUS score is: " + (a*1000));
                break;
            default:
                Console.WriteLine("Invalid Score!");
                break;
 
        }
    }
}