Considering Unknown Cases

Switching to a Null Case

When working on a switch statement, you may have a situation where the variable considered is not holding a known value or its value is clearly null. In this situation, the C# language allows you to consider a case that is null. To do this, in the switch statement, create a case whose value is null. Here is an example:

using System.Windows.Forms;

namespace Chemistry
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            Element elm = Create();

            txtSymbol.Text = elm.Symbol;
            txtAtomicNumber.Text = elm.AtomicNumber.ToString();
            txtElementName.Text = elm.ElementName;
            txtAtomicWeight.Text = elm.AtomicWeight.ToString();
            txtPhase.Text = elm.Phase.ToString();
        }

        Element Create()
        {
            int? number = null;
            Element selected = null;

            Element b = new Element(5, "B", "Boron", 10.81, Phase.Solid);
            Element h = new Element(1, "H", "Hydrogen", 1.008, Phase.Gas);
            Element he = new Element(2, "He", "Helium", 4.002602, Phase.Gas);
            Element li = new Element(3, "Li", "Lithium", 6.94, Phase.Solid);
            Element be = new Element(4, "Be", "Beryllium", 9.0121831, Phase.Solid);

            switch (number)
            {
                case 2:
                    selected = he;
                    break;
                case 3:
                    selected = li;
                    break;
                case 4:
                    selected = be;
                    break;
                case 5:
                    selected = b;
                    break;
                case null:
                    selected = h;
                    break;
            }

            return selected;
        }
    }

    public enum Phase { Gas, Liquid, Solid, Unknown }

    public class Element
    {
        public string Symbol { get; set; }
        public string ElementName { get; set; }
        public int AtomicNumber { get; set; }
        public double AtomicWeight { get; set; }
        public Phase Phase { get; set; }

        public Element(int number, string symbol, string name, double mass, Phase phase)
        {
            ElementName = name;
            AtomicWeight = mass;
            Phase = phase;
            Symbol = symbol;
            AtomicNumber = number;
        }
    }
}

By the way, the null case can be the first, it can be the last, or it can appear in any position within the switch statment.

Switching to the default Outcome

When considering the possible outcomes of a switch statement, at times there will be possibilities other than those listed and you will be likely to consider them. This special case is handled by the default keyword. The default case would be considered if none of the listed cases matches the supplied answer. The formula of the switch statement that considers the default case is:

switch(expression)
{
    case choice1:
        statement1;
    	break;
    case choice2:
        statement2;
    	break;
    case choice-n:
        statement-n;
    	break;
    default:
        default-statement;
    	break;
}

In some languages, the default section doesn't require a break keyword because it is the last. In C#, every case and the default section must have its own exit mechanism, which is taken care of by a break keyword.

Practical Learning: Switching to a Default Outcome

1. Start Microsoft Visual Studio. On the Visual Studio 2019 dialog box, click Create a New Project and click Next (if Microsoft Visual Studio was already opened, on the main menu, click File -> New -> Project...)
2. In the list of projects templates, click Windows Forms App (.NET Framework)
3. Click Next
4. Change the project Name to PayrollPreparation06
5. Click Create
6. In the Solution Explorer, right-click Form1.cs -> Rename
7. Type PayrollEvaluation to get PayrollEvaluation.cs
8. Press Enter twice
9. In the Toolbox, under Common Controls, click ComboBox
10. Click the form
11. While the combo box is selected on the form, in the Properties window, click Items and click its button
12. In the text box of the String Collection Editor, type each of the following strings:

    Nothing
    Utah
    Illinois
    Indiana
    Michigan
    Colorado
    Pennsylvania
    North Carolina

    

13. Click OK
14. Complete the design of the form as follows:

    

    Control	(Name)	Text	TextAlign
    Label		Gross Salary:
    TextBox	txtGrossSalary	0	Right
    Label		State:
    ComboBox	cbxStates
    Button	btnCalculate	Calculate
    Label		txtEmployeeResidence
    TextBox	txtEmployeeResidence		Right
    Label		txtIncomeTax
    TextBox			Right
    Label		Net Pay:
    TextBox	txtNetPay		Right

15. Double-click the Calculate button
16. Right-click inside the Code Editor and click Remove and Sort Usings
17. Change the code as follows:

    using System;
    using System.Windows.Forms;
    
    namespace PayrollEvaluation06
    {
        public partial class PayrollEvaluation : Form
        {
            public PayrollEvaluation()
            {
                InitializeComponent();
            }
    
            private void btnCalculate_Click(object sender, EventArgs e)
            {
    
                double taxes = 0.00;
                string residence = "";
    
                string state = cbxStates.Text;
                double salary = Convert.ToDouble(txtGrossSalary.Text);
    
                switch (state)
                {
                    case "Colorado":
                        taxes = salary * 4.63 / 100.00;
                        residence = "Colorado (4.63%)";
                        break;
                    case "Illinois":
                        taxes = salary * 3.75 / 100.00;
                        residence = "Illinois (3.75%)";
                        break;
                    case "Indiana":
                        taxes = salary * 3.3 / 100.00;
                        residence = "Indiana (3.3%)";
                        break;
                    case "Michigan":
                        taxes = salary * 4.25 / 100.00;
                        residence = "Michigan (4.25%)";
                        break;
                    case "North Carolina":
                        taxes = salary * 5.75 / 100.00;
                        residence = "North Carolina (5.75%)";
                        break;
                    case "Pennsylvania":
                        taxes = salary * 3.07 / 100.00;
                        residence = "Pennsylvania (3.07%)";
                        break;
                    case "Utah":
                        taxes = salary * 5 / 100.00;
                        residence = "Utah (5%)";
                        break;
                    default:
                        taxes = 0.00;
                        residence = "";
                        break;
                }
    
                txtEmployeeResidence.Text = residence;
                txtStateIncomeTax.Text = taxes.ToString("F");
                txtNetPay.Text = (salary - taxes).ToString("F");
            }
        }
    }

18. To execute the application, on the main menu,, click Debug -> Start Without Debugging
19. In the Gross Salary text box, type a number such as 3266.48
20. In the combo box, select a state, such as Pennsylvania:

    

21. Click the Calculate button:

    

22. Close the form and return to your programming environment
23. On the main menu of Microsoft Visual Studio, click File -> New -> Project...
24. In the list of projects templates, click Windows Forms App (.NET Framework)
25. Click Next
26. Change the project Name to Chemistry08
27. Click Add
28. On the main menu, click Project -> Add Class...
29. Replace the name with Element
30. Click Add
31. Change the code as follows:

    namespace Chemistry08
    {
        public enum Phase { Gas, Liquid, Solid, Unknown }
    
        public class Element
        {
            public string Symbol       { get; set; }
            public string ElementName  { get; set; }
            public int    AtomicNumber { get; set; }
            public double AtomicWeight { get; set; }
            public Phase  Phase        { get; set; }
    
            public Element()                 { }
            public Element(int number)    => AtomicNumber = number;
            public Element(string symbol) => Symbol = symbol;
    
            public Element(int number, string symbol, string name, double mass, Phase phase)
            {
                ElementName = name;
                AtomicWeight = mass;
                Phase = phase;
                Symbol = symbol;
                AtomicNumber = number;
            }
        }
    }

32. In the Solution Explorer, right-click Form1.cs -> Rename
33. Type Chemistry to get Chemistry.cs
34. Press Enter three times (to accept the name and access the form
35. Design the form as follows:

    

    Control	(Name)	Text
    Label		Enter Atomic Number::
    TextBox	txtNumberEntered
    Button	btnFind	Find
    GroupBox		Element Detais
    Label		Atomic Number:
    TextBox	txtAtomicNumber
    Label		Symbol:
    TextBox	txtSymbol
    Label		Element Name:
    TextBox	txtElementName
    Label		Atomic Weight:
    TextBox	txtAtomicWeight
    Label		Phase:
    TextBox	txtPhase

36. Double-click the Find button
37. Right-click inside the Code Editor and click Remove and Sort Usings

Considering Default and Null Cases

When creating a switch statement, you should predict as many cases as possible. We already know that you can create a default case that would embrace the value that matches none of the others; but the default case assumes that there is a valid value that none of the other cases is holding. We saw that this is not always the case: there could be an unknown or invalid value. For example, you can consider a series of numbers from 10, in which case 12 is not included but 12 is a valid value; but a null case would mean that you don't have a number at all. For this type of scenario, you should consider using both a null and a default cases. By the way, those cases can appear in any order.

Practical Learning: Considering Default and Null Cases

1. Change the document as follows:

   using System;
   using System.Windows.Forms;
   
   namespace Chemistry08
   {
       public partial class Chemistry : Form
       {
           public Chemistry()
           {
               InitializeComponent();
           }
   
           Element SelectElement()
           {
               Element H = new Element(1, "H", "Hydrogen", 1.008, Phase.Gas);
               Element He = new Element(2, "He", "Helium", 4.002602, Phase.Gas);
               Element Li = new Element(3, "Li", "Lithium", 6.94, Phase.Solid);
               Element Be = new Element(4, "Be", "Beryllium", 9.0121831, Phase.Solid);
               Element B = new Element(5, "B", "Boron", 10.81, Phase.Solid);
               Element C = new Element(name: "Carbon", mass: 12.011, symbol: "C", number: 6, phase: Phase.Solid);
               Element N = new Element(7);
               N.Symbol = "N"; N.AtomicWeight = 14.007;
               N.ElementName = "Nitrogen"; N.Phase = Phase.Gas;
               Element O = new Element("O") { AtomicNumber = 8, ElementName = "Oxygen",
                                              AtomicWeight = 15.999, Phase = Phase.Gas };
               Element F = new Element("F") { AtomicNumber = 9, ElementName = "Fluorine",
                                              AtomicWeight = 15.999, Phase = Phase.Gas };
               Element Ne = new Element("Ne") { AtomicNumber = 10, ElementName = "Neon",
                                                AtomicWeight = 20.1797, Phase = Phase.Gas };
               Element Na = new Element(11, "Na", "Sodium", 22.98976928, Phase.Solid);
               Element Mg = new Element(12, "Mg", "Magnesium", 24.305, Phase.Solid);
               Element Al = new Element(13, "Al", "Aluminium", 26.9815385, Phase.Solid);
               Element Si = new Element() { ElementName = "Silicon", AtomicWeight = 28.085, Symbol = "Si", AtomicNumber = 14, Phase = Phase.Solid };
               Element P  = new Element()  { ElementName = "Phosphorus", AtomicWeight = 30.973761998, Symbol = "P", AtomicNumber = 15, Phase = Phase.Solid };
               Element S  = new Element(16, "S", "Sulfur", 32.06, Phase.Solid);
               Element Cl = new Element() { AtomicWeight = 35.446, Symbol = "Cl", ElementName = "Chlorine", AtomicNumber = 17, Phase = Phase.Gas };
               Element Ar = new Element() { ElementName = "Argon", AtomicWeight = 39.792, Symbol = "Ar", AtomicNumber = 18, Phase = Phase.Gas };
               Element K  = new Element() { ElementName = "Potassium", Symbol = "K", Phase = Phase.Solid, AtomicWeight = 39.0983, AtomicNumber = 19 };
               Element Ca = new Element() { Symbol = "Ca", Phase = Phase.Solid, AtomicNumber = 20, ElementName = "Calcium", AtomicWeight = 40.078 };
               Element Sc = new Element() { AtomicNumber = 21, Symbol = "Sc", AtomicWeight = 44.9559085, Phase = Phase.Solid, ElementName = "Scandium" };
               Element Ti = new Element() { ElementName = "Titanium", AtomicWeight = 47.8671, Symbol = "Ti", AtomicNumber = 22, Phase = Phase.Solid };
   
               Element selected;
               int? number = null;
   
               if (txtNumberEntered.Text == "")
                   number = null;
               else
                   number = int.Parse(txtNumberEntered.Text);
   
               switch (number)
               {
                   case 8:
                       selected = O;
                       break;
                   case 19:
                       selected = K;
                       break;
                   case 7:
                       selected = N;
                       break;
                   case 9:
                       selected = F;
                       break;
                   case 16:
                       selected = S;
                       break;
                   case 3:
                       selected = Li;
                       break;
                   case 6:
                       selected = C;
                       break;
                   case 10:
                       selected = Ne;
                       break;
                   case 5:
                       selected = B;
                       break;
                   default:
                       selected = H;
                       break;
                   case null:
                       selected = new Element(0, "", "Known", 0.00, Phase.Unknown); ;
                       break;
                   case 11:
                       selected = Na;
                       break;
                   case 2:
                       selected = He;
                       break;
                   case 12:
                       selected = Mg;
                       break;
                   case 4:
                       selected = Be;
                       break;
                   case 13:
                       selected = Al;
                       break;
                   case 21:
                       selected = Sc;
                       break;
                   case 14:
                       selected = Si;
                       break;
                   case 20:
                       selected = Ca;
                       break;
                   case 15:
                       selected = P;
                       break;
                   case 22:
                       selected = Ti;
                       break;
                   case 18:
                       selected = Ar;
                       break;
                   case 17:
                       selected = Cl;
                       break;
               }
   
               return selected;
           }
   
           void Display(Element ce)
           {
               txtSymbol.Text = ce.Symbol;
               txtAtomicNumber.Text = ce.AtomicNumber.ToString();
               txtElementName.Text = ce.ElementName;
               txtAtomicWeight.Text = ce.AtomicWeight.ToString();
               txtPhase.Text = ce.Phase.ToString();
           }
   
           private void btnFind_Click(object sender, EventArgs e)
           {
               Element elm = SelectElement();
   
               Display(elm);
           }
       }
   }

2. To execute the project, on the main menu, click Debug -> Start Without Debugging:

   

3. In the top text box, type a number between 1 (included) and 22 (included). Here is an example:

   

4. Click the Find button:

   

5. Close the form and return to your programming environment
6. On the main menu of Microsoft Visual Studio, click File -> Recent Projects and Solutions -> ... PayrollEvaluation06
7. Click the PayrollEvaluation.cs [Design] tab to access the form
8. On the form, right-click the combo box -> Edit Items...
9. Change the list to become as follows:

   Nothing
   Utah
   Texas
   Alaska
   Nevada
   Florida
   Indiana
   Wyoming
   Illinois
   Michigan
   Colorado
   Tennessee
   Washington
   Pennsylvania
   South Dakota
   New Hampshire
   North Carolina

10. Click OK
11. In the Properties, change the Text of the form to State Income Tax
12. Right-click the form and click View Code

Cases Combinations

Introductions

Although each case must consider only one value, you may have a situation where different case values must deal with the same outcome. In this case, you can combine those cases. To do this, type case followed by its value and a colon. On the next line, create another case with its value and colon. You can continue that for each value that fits that group. Then write the common code of those cases and end the section with the required break keyword and its semicolon.

Practical Learning: Combining Cases in a Switch

1. Change the code of the event as follows:

   using System;
   using System.Windows.Forms;
   
   namespace PayrollEvaluation06
   {
       public partial class PayrollEvaluation : Form
       {
           public PayrollEvaluation()
           {
               InitializeComponent();
           }
   
           private void btnCalculate_Click(object sender, EventArgs e)
           {
   
               double taxes = 0.00;
               string residence = "";
   
               string state = cbxStates.Text;
               double salary = Convert.ToDouble(txtGrossSalary.Text);
   
               switch (state)
               {
                   case "Colorado":
                       taxes = salary * 4.63 / 100.00;
                       residence = "Colorado (4.63%)";
                       break;
                   case "Alaska":
                   case "Florida":
                       // Two of the 9 states that don't collect an income tax
                       taxes = 0.00;
                       residence = "No Income Tax";
                       break;
                   case "Illinois":
                       taxes = salary * 3.75 / 100.00;
                       residence = "Illinois (3.75%)";
                       break;
                   case "Indiana":
                       taxes = salary * 3.3 / 100.00;
                       residence = "Indiana (3.3%)";
                       break;
                   case "Nevada":
                   case "New Hampshire":
                   case "Tennessee":
                   case "Texas":
                       // Four other states that don't collect an income tax
                       taxes = 0.00;
                       residence = "Income Tax Not Collected";
                       break;
                   case "Michigan":
                       taxes = salary * 4.25 / 100.00;
                       residence = "Michigan (4.25%)";
                       break;
                   case "North Carolina":
                       taxes = salary * 5.75 / 100.00;
                       residence = "North Carolina (5.75%)";
                       break;
                   case "South Dakota":
                   case "Washington":
                   case "Wyoming":
                       // Three other states that don't collect an income tax
                       taxes = 0.00;
                       residence = "Income Tax Not Paid";
                       break;
                   case "Pennsylvania":
                       taxes = salary * 3.07 / 100.00;
                       residence = "Pennsylvania (3.07%)";
                       break;
                   case "Utah":
                       taxes = salary * 5 / 100.00;
                       residence = "Utah (5%)";
                       break;
                   default:
                       taxes = 0.00;
                       residence = "";
                       break;
               }
   
               txtEmployeeResidence.Text = residence;
               txtStateIncomeTax.Text = taxes.ToString("F");
               txtNetPay.Text = (salary - taxes).ToString("F");
           }
       }
   }

2. To execute the application to test it, press Ctrl + F5
3. In the Gross Salary text box, type a number such as 2814.83
4. In the combo box, select a state, such as South Dakota, Wyoming, Tenessee, Alaska, Nevada, Texas, Washington, Florida, or New Hampshire:

   

5. Click the Calculate button:

   

6. Close the form and return to your programming environment

Nesting a Conditional Statement in a Case

Each case of a switch statement has its own body in which you can create a conditional statement. This is referred to as nesting.

Practical Learning: Nesting a Conditional Statement in a Case

1. On the main menu of Microsoft Visual Studio, click File -> New -> Project...
2. In the list of projects templates, click Windows Forms App (.NET Framework)
3. Click Next
4. Change the project Name to PayrollPreparation07
5. Click Create
6. Design the form as follows:

   

   Control	(Name)	Text	Other Properties
   Label		Gross Salary:
   TextBox	txtGrossSalary	0	TextAlign: Right
   Label		Filing As:
   ComboBox	cbxFilingAs		Items: Single Married
   Label		Exemptions:
   TextBox	txtExemptions
   Button	btnCalculate	Calculate
   Label		Filing Status:
   TextBox	txtFilingStatus		TextAlign: Right
   Label		Allowances
   TextBox	txtAllowances		TextAlign: Right
   Label		Taxable Gross Wages:
   TextBox	txtTaxableGrossWages		TextAlign: Right
   Label		Federal Income Tax:
   TextBox	txtFederalIncomeTax		TextAlign: Right

7. Double-click the Calculate button
8. Right-click inside the Code Editor and click Remove and Sort Usings
9. Type Views and press Enter
10. Type Home and press Enter
11. In the Solution Explorer, right-click Home -> Add -> New Item...
12. Change the code as follows:

    using System;
    using System.Windows.Forms;
    
    namespace PayrollPreparation7
    {
        public partial class Form1 : Form
        {
            public Form1()
            {
                InitializeComponent();
            }
    
            private void btnCalculate_Click(object sender, EventArgs e)
            {
                double withheldAmount = 0;
                double allowanceRate = 77.90;
                double salary = double.Parse(txtGrossSalary.Text);
                string filingStatus = cbxFilingStatus.Text;
                int exemptions = int.Parse(txtExemptions.Text);
    
                double withheldingAllowances = allowanceRate * exemptions;
                double taxableGrossWages = salary - withheldingAllowances;
    
                switch (filingStatus)
                {
                    case "Single":
                        if (taxableGrossWages <= 44)
                        {
                            withheldAmount = 0;
                        }
                        else if ((taxableGrossWages > 44.00) && (taxableGrossWages <= 224.00))
                        {
                            withheldAmount = (taxableGrossWages - 44.00) * 10.00 / 100;
                        }
                        else if ((taxableGrossWages > 224.00) && (taxableGrossWages <= 774.00))
                        {
                            withheldAmount = 18.00 + ((taxableGrossWages - 224.00) * 15.00 / 100);
                        }
                        else if ((taxableGrossWages > 774.00) && (taxableGrossWages <= 1812.00))
                        {
                            withheldAmount = 100.50 + ((taxableGrossWages - 774.00) * 25.00 / 100);
                        }
                        else if ((taxableGrossWages > 1812.00) && (taxableGrossWages <= 3730))
                        {
                            withheldAmount = 360.00 + ((taxableGrossWages - 1812.00) * 28.00 / 100);
                        }
                        else if ((taxableGrossWages > 3730.00) && (taxableGrossWages <= 8058.00))
                        {
                            withheldAmount = 897.04 + ((taxableGrossWages - 3730.00) * 33.00 / 100);
                        }
                        else if ((taxableGrossWages > 8058.00) && (taxableGrossWages <= 8090.00))
                        {
                            withheldAmount = 2325.28 + ((taxableGrossWages - 8058) * 35.00 / 100);
                        }
                        else // if (taxableGrossWages > 8090.00)
                        {
                            withheldAmount = 2336.48 + ((taxableGrossWages - 8090.00) * 39.60 / 100);
                        }
    
                        break;
    
                    case "Married":
                        if (taxableGrossWages <= 166.00)
                        {
                            withheldAmount = 0;
                        }
                        else if ((taxableGrossWages > 166.00) && (taxableGrossWages <= 525.00))
                        {
                            withheldAmount = (taxableGrossWages - 166.00) * 10.00 / 100;
                        }
                        else if ((taxableGrossWages > 525.00) && (taxableGrossWages <= 1626.00))
                        {
                            withheldAmount = 35.90 + ((taxableGrossWages - 525.00) * 15.00 / 100);
                        }
                        else if ((taxableGrossWages > 1626.00) && (taxableGrossWages <= 3111.00))
                        {
                            withheldAmount = 201.05 + ((taxableGrossWages - 1626.00) * 25.00 / 100);
                        }
                        else if ((taxableGrossWages > 3111.00) && (taxableGrossWages <= 4654.00))
                        {
                            withheldAmount = 572.30 + ((taxableGrossWages - 3111.00) * 28.00 / 100);
                        }
                        else if ((taxableGrossWages > 4654.00) && (taxableGrossWages <= 8180.00))
                        {
                            withheldAmount = 1004.34 + ((taxableGrossWages - 4654.00) * 33.00 / 100);
                        }
                        else if ((taxableGrossWages > 8160.00) && (taxableGrossWages <= 9218.00))
                        {
                            withheldAmount = 2167.92 + ((taxableGrossWages - 8180.00) * 35.00 / 100);
                        }
                        else // if (taxableGrossWages > 9218)
                        {
                            withheldAmount = 2531.22 + ((taxableGrossWages - 9218.00) * 39.60 / 100);
                        }
                        break;
                }
    
                txtFilingStatus.Text = filingStatus;
                txtAllowances.Text = withheldingAllowances.ToString("F");
                txtTaxableGrossWages.Text = taxableGrossWages.ToString("F");
                txtFederalIncomeTax.Text = withheldAmount.ToString("F");
            }
        }
    }

13. To execute the project, on the main menu, click Debug -> Start Without Debugging

    

14. Click the Single radio button and set the Salary to 1488.72
15. In the combo box, select an option, such as Married
16. In the Exemptions text box, type a small number such as 3

    

17. Click the Calculate button:

    

18. Process another tax calculation for a Single person with 2 exemptions and a salary of 3618.76. Then click the Calculate button:

    

19. Close the form and return to your programming environment

Pattern Matching

When Switching a Value

So far, we have seen that, when you are setting up a switch statement, create the desired case clauses in the switch section. The case keyword can be followed by either a constant value or an expression. Here are examples:

switch (number)
{
    case 1:
        selected = h;
        break;
    case 2:
        selected = he;
        break;
    case 3:
        selected = li;
        break;
}

Pattern matching consists of applying a condition to a case. In a case of a switch statement, you can include a conditional statement that compares its value to another to actually validate the case. This is done using the when keyword. The formula to follow is:

case value-or-expression when logical-expression: statement(s)

As mentioned already, the case is followed by a constant or an expression, The new keyword is when. It is followed by a logical expression.

When Switching a Variable

After a case keyword, you can declare a variable of the same type as the value used in the parentheses of switch(). Follow the variable with the when keyword followed by a logical expression that equates the variable to the case value. The variable is "visible" only with its case. Therefore, you can use the same variable in different case sections.

When Patterning a Conditional Statement

The when expression is used to apply a conditional statement. It can consist of an expression that uses any of the Boolean operators we are familiar with. It may look as follows:

switch(number)
{
    case value-or-expression when number > 8:
        statement(s);
        break;
}

Patterning Different Types of Values

When using a switch statement, the values involved must be of the same type or compatible. Otherwise, you can find a way to convert them.

Practical Learning: Ending the Lesson

• Close your programming environment

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