Functions Fundamentals

Introduction

As seen in our first introduction to methods, a function is a section of code that performs an action. You create a function by writing code. The fundamental formula to follow when creating a function is:

options function-name(...)
{
}

As you may know already, code in C# must be written inside an object layout, such as a class (or a structure). In C#, console and Windows Forms applications don't allow functions (created outside a class (or structures)), but other types of C# applications, such as web applications, allow functions. In our series of lessons here, a function is a section of code that behaves like it is created and used outside a class. In other words, we use functions here as indipendent entities, that is independent from a class.

Practical Learning: Introducing Functions

1. Start Microsoft Visual Studio. In the Visual Studio 2019 dialog box, click Create a New Project (if Microsoft Visual Studio was already opened, on the main menu, click File -> New -> Project...)
2. In the Create a New Project dialog box, in the list of projects templates, click Windows Forms App (.NET Framework)
3. Click Next
4. Change the name to SalaryEvaluation1
5. Click Create
6. Design the form as follows:

   

   Control	(Name)	Text
   Label		Hourly Salary:
   TextBox	txtHourlySalary	0.00
   Button	btnCalculate	Calculate
   Label		_______________________
   Label		Daily Salary:
   TextBox	txtDailySalary
   Label		Weekly Salary:
   TextBox	txtWeeklySalary
   Label		Biweekly Salary:
   TextBox	txtBiweeklySalary
   Label		Monthly Salary:
   TextBox	txtMonthlySalary
   Label		Yearly Salary:
   TextBox	txtYearlySalary

7. Right-click the body of the form and click View Code
8. Right-click in the Code Editor and click Remove and Sort Usings

A Void Function

The creation of a function starts with some options. Later, we will learn more about them in next sections and lessons. For a simple function, specify the option with the void keyword.

The Name of a Function

A function must have a name. That name must follow some rules:

• The name of a function can be a single letter. By tradition, that letter should be in uppercase
• The name of a function can be a word. If the name of a function is a word, the first letter should be in uppercase
• he name of a function can be a combination of words. If the name of a method is a combination of words, the first letter of each word should be in uppercase
• Because a function is an action, its name should resemble a verb

The Parentheses of a Function

The name of a function is followed by parentheses. At a minimum, the parentheses can be empty. Most of the time, you will writteen the parentheses on the same line as the name of the function. Otherwise, you can write each parenthesis on its own line. Here is an example:

void HelpMe
(
)

Or like this:

void HelpMe(
           )

Or like this:

void HelpMe
     (
     )

The Body of a Function

The body of a function follows the parentheses. After the parentheses, add some brackets { and }. The section between the curly brackets is the body of the function. In that body, you can write the code that describes what the function is supposed to do.

Practical Learning: Creating a Fuction

1. Change the code as follows:

   using System.Windows.Forms;
   
   namespace SalaryEvaluation1
   {
       public partial class Form1 : Form
       {
           public Form1()
           {
               InitializeComponent();
           }
   
           void PresentValues()
           {
               double hourlySalary = double.Parse(txtHourlySalary.Text);
   
               double dailySalary = hourlySalary * 8;
               double weeklySalary = hourlySalary * 40;
               double biweeklySalary = weeklySalary * 2;
               double monthlySalary = weeklySalary * 4;
               double yearlySalary = monthlySalary * 12;
   
               txtDailySalary.Text = dailySalary.ToString();
               txtWeeklySalary.Text = weeklySalary.ToString();
               txtBiweeklySalary.Text = biweeklySalary.ToString();
               txtMonthlySalary.Text = monthlySalary.ToString();
               txtYearlySalary.Text = yearlySalary.ToString();
           }
       }
   }

2. Click the Form1.cs [Design] tab to access the form
3. On the form, double-click the Calculate button

Calling a Function

After creating a function, you can use it. Using a function is referred to as calling it. To call a simple like the one we created above, type its name, followed by parentheses, and it with a semicolon.

Practical Learning: Calling a Function

1. Implement the event as follows:

   using System.Windows.Forms;
   
   namespace SalaryEvaluation1
   {
       public partial class Form1 : Form
       {
           public Form1()
           {
               InitializeComponent();
           }
   
           void PresentValues
                (
                )
           {
               double hourlySalary = double.Parse(txtHourlySalary.Text);
   
               double dailySalary = hourlySalary * 8;
               double weeklySalary = hourlySalary * 40;
               double biweeklySalary = weeklySalary * 2;
               double monthlySalary = weeklySalary * 4;
               double yearlySalary = monthlySalary * 12;
   
               txtDailySalary.Text = dailySalary.ToString();
               txtWeeklySalary.Text = weeklySalary.ToString();
               txtBiweeklySalary.Text = biweeklySalary.ToString();
               txtMonthlySalary.Text = monthlySalary.ToString();
               txtYearlySalary.Text = yearlySalary.ToString();
           }
   
           private void btnCalculate_Click(object sender, System.EventArgs e)
           {
               PresentValues();
           }
       }
   }

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

   

3. In the Hourly Salary text box, type 22.38
4. Click the Calculate button:

   

5. Close the form and return to your programming environment
6. On the main menu of Microsoft Visual Studio, click File -> New -> Project...
7. In the list of projects templates, click Windows Forms App (.NET Framework)
8. Click Next
9. Change the project Name to WaterCompany5
10. Click Create
11. Design the form as follows:

    

    Control	(Name)	Text
    Label		Meter Reading Start . . . . . . . . . . . .
    TextBox	txtMeterReadingStarStart	0
    Label		Gallons
    Label		Meter Reading End . . . . . . . . . . . .
    TextBox	txtMeterReadingStarEnd	0
    Label		Gallons
    Button	btnCalculateWaterAndSewerUsage	Calculate Water and Sewer Usage
    Label		_______________________________
    Label		Water and Sewer Usage . . . . . . . . . . . .
    TextBox	txtWaterSewerUsage	0
    Label		Gallons
    Label		Water Use Charges => 4.18 per 1,000 Gallons . . . . . . . . . . . . . . . . . . . . . .
    TextBox	txtSewerUseCharges	0.00
    Label		Sewer Use Charges => 5.85 per 1,000 Gallons . . . . . . . . . . . . . . . . . . . . .
    TextBox	txtSewerUseCharges	0.00

12. On the form, double-click the Calculate Water and Sewer Usage button
13. To create another function and call it, change the document as follows:

    using System.Windows.Forms;
    
    namespace WaterCompany5
    {
        public partial class Form1 : Form
        {
            public Form1()
            {
                InitializeComponent();
            }
    
            void CalculteWaterSewer()
            {
                double usage;
    
                double meterReadingStart = int.Parse(txtMeterReadingStart.Text);
                double meterReadingEnd = int.Parse(txtMeterReadingEnd.Text);
    
                usage = meterReadingEnd - meterReadingStart;
    
                double waterConsumption = (usage * 4.18) / 1000;
                double sewerServices = (usage * 5.85) / 1000;
    
                txtWaterSewerUsage.Text = usage.ToString();
                txtWaterUseCharges.Text = waterConsumption.ToString("F");
                txtSewerUseCharges.Text = sewerServices.ToString("F");
            }
    
            private void btnCalculateWaterAndSewerUsage_Click(object sender, System.EventArgs e)
            {
                CalculteWaterSewer();
            }
        }
    }

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

    

15. In the top text box, type a large number of gallons such as 4017
16. In the second text box, type a number higher than the first one, such as 6249
17. Click the top Calculate button:

    

18. Change the design of the form as follows:

    

    Control	(Name)	Text
    Label		Meter Reading Start . . . . . . . . . . . .
    TextBox	txtMeterReadingStarStart	0
    Label		Gallons
    Label		Meter Reading End . . . . . . . . . . . .
    TextBox	txtMeterReadingStarEnd	0
    Label		Gallons
    Button	btnCalculateWaterAndSewerUsage	Calculate Water and Sewer Usage
    Label		_______________________________
    Label		Water and Sewer Usage . . . . . . . . . . . .
    TextBox	txtWaterSewerUsage	0
    Label		Gallons
    Label		Water Use Charges => 4.18 per 1,000 Gallons . . . . . . . . . . . . . . . . . . . . . .
    TextBox	txtSewerUseCharges
    Label		Sewer Use Charges => 5.85 per 1,000 Gallons . . . . . . . . . . . . . . . . . . . . .
    TextBox	txtSewerUseCharges
    Label		Distribution Charges . . . . . . . . . . . . . .
    TextBox	txtDistributionCharges	0.00
    Label		Environment Charges . . . . . . . . . . . . . .
    TextBox	txtEnvironmentCharges	0.00
    Button	btnCalculateTotalCharges	Calculate Total Charges
    Label		_______________________________
    Label		Total Charges . . . . . . . . . . . .
    TextBox	txtTotalCharges

19. Click the Form1.cs tab to access the code of the form

A Function that Returns a Value

A Function that Returns Nothing

Practially every function has a body, which is delimited by curly brackets. Still, to indicate the end of execution of a function, type the return keyword followed by a semicolon. Here are examples:

class Exercise
{
	void Communicate()
    {
    	return;
    }
    
    void NeedToDiscuss()
    {
    	return;
    }
    
	static void Main()
    {
    	return;
    }
}

Introduction to Returning a Value

Sometimes, you will want a function that gives back a value from its operation(s). To start, when creating the function, on the left side of the name of the function, instead of void, write the data type of the value that the function will produce. Here is an example:

int Calculate()
{
}

In the body of the function, perform the necessary operation. Before the closing curly bracket, type the return keyword, followed by the value the function must return, and end the statement with a semicolon.

Practical Learning: Returning a Value from a Function

1. Create a new function as follows:

   using System.Windows.Forms;
   
   namespace WaterCompany5
   {
       public partial class Form1 : Form
       {
           public Form1()
           {
               InitializeComponent();
           }
   
           void CalculteWaterSewer(
                                  )
           {
               double usage;
   
               double meterReadingStart = int.Parse(txtMeterReadingStart.Text);
               double meterReadingEnd = int.Parse(txtMeterReadingEnd.Text);
   
               usage = meterReadingEnd - meterReadingStart;
   
               double waterConsumption = (usage * 4.18) / 1000;
               double sewerServices = (usage * 5.85) / 1000;
   
               txtWaterSewerUsage.Text = usage.ToString();
               txtWaterUseCharges.Text = waterConsumption.ToString("F");
               txtSewerUseCharges.Text = sewerServices.ToString("F");
           }
   
           private void btnCalculateWaterAndSewerUsage_Click(object sender, System.EventArgs e)
           {
               CalculteWaterSewer();
           }
   
           double CalculateSewerUsage()
           {
               double amountDue;
               double waterUseCharges;
               double sewerUseCharges;
               double distributionCharges;
               double environmentCharges;
   
               waterUseCharges = double.Parse(txtWaterUseCharges.Text);
               sewerUseCharges = double.Parse(txtSewerUseCharges.Text);
               distributionCharges = double.Parse(txtDistributionCharges.Text);
               environmentCharges = double.Parse(txtEnvironmentCharges.Text);
   
               amountDue = waterUseCharges + sewerUseCharges + distributionCharges + environmentCharges;
   
               return amountDue;
           }
       }
   }

2. Click the Form1.cs [Design] tab to access the form

Calling a Function that Returns a Value

You can call a function that returns a value as you do for one that is void. If you want to get and use the value returned by the function, you can declare a variable of the return type and assign the call to that variable. The variable would then be carrying the return value of the function and you can use that value any way you want.

Practical Learning: Calling a Function that Returns a Value

1. On the form, double-click the Calculate Total Charges button
2. In the event, call the function as follows:

   using System.Windows.Forms;
   
   namespace WaterCompany5
   {
       public partial class Form1 : Form
       {
           public Form1()
           {
               InitializeComponent();
           }
   
           void CalculteWaterSewer
                                  (
                                  )
           {
               double usage;
   
               double meterReadingStart = int.Parse(txtMeterReadingStart.Text);
               double meterReadingEnd = int.Parse(txtMeterReadingEnd.Text);
   
               usage = meterReadingEnd - meterReadingStart;
   
               double waterConsumption = (usage * 4.18) / 1000;
               double sewerServices = (usage * 5.85) / 1000;
   
               txtWaterSewerUsage.Text = usage.ToString();
               txtWaterUseCharges.Text = waterConsumption.ToString("F");
               txtSewerUseCharges.Text = sewerServices.ToString("F");
           }
   
           private void btnCalculateWaterAndSewerUsage_Click(object sender, System.EventArgs e)
           {
               CalculteWaterSewer();
           }
   
           double CalculateSewerUsage()
           {
               double amountDue;
               double waterUseCharges;
               double sewerUseCharges;
               double distributionCharges;
               double environmentCharges;
   
               waterUseCharges = double.Parse(txtWaterUseCharges.Text);
               sewerUseCharges = double.Parse(txtSewerUseCharges.Text);
               distributionCharges = double.Parse(txtDistributionCharges.Text);
               environmentCharges = double.Parse(txtEnvironmentCharges.Text);
   
               amountDue = waterUseCharges + sewerUseCharges + distributionCharges + environmentCharges;
   
               return amountDue;
           }
   
           private void btnCalculateTotalCharges_Click(object sender, System.EventArgs e)
           {
               double invoice = CalculateSewerUsage();
   
               txtTotalCharges.Text = invoice.ToString();
           }
       }
   }

3. To execute the application, on the main menu, click Debug -> Start Without Debugging
4. In the top text box, type a large number of gallons such as 4017
5. In the second text box, type a number higher than the first one, such as 6249
6. Click the top Calculate button
7. In the Distribution Charges text box, type a number such as 12.57
8. In the Environment Charges text box, type a number such as 24.83
9. Click the bottom Calculate button
10. Close the form and return to your programming environment
11. You first declare a variable if you think that will need to use the value of the function many times. If you will need to use the value returned by the function only once, you may not need a variable. You can call the function directly where its value is returned. For an example, change the code as follows:

    using System.Windows.Forms;
    
    namespace WaterCompany5
    {
        public partial class Form1 : Form
        {
            public Form1()
            {
                InitializeComponent();
            }
    
            void CalculteWaterSewer()
            {
                . . .
            }
    
            private void btnCalculateWaterAndSewerUsage_Click(object sender, System.EventArgs e)
            {
                CalculteWaterSewer();
                
                // The following line is optional
                return;
            }
    
            double CalculateSewerUsage()
            {
                . . .
    
                return amountDue;
            }
    
            private void btnCalculateTotalCharges_Click(object sender, System.EventArgs e)
            {
                txtTotalCharges.Text = CalculateSewerUsage().ToString();
                
                // The following line is optional
                return;
            }
        }
    }

12. To execute, press Ctrl + F5
13. Close the form and return to your programming environment
14. On the main menu of Microsoft Visual Studio, click File -> New -> Project...
15. In the Create a New Project dialog box, in the list of projects templates, click Windows Forms App (.NET Framework)
16. Click Next
17. Change the name to SalaryEvaluation2
18. Click Create
19. Design the form as follows:

    

    Control	(Name)	Text
    Label		Hourly Salary:
    TextBox	txtHourlySalary	0.00
    Button	btnCalculate	Calculate
    Label		_______________________
    Label		Daily Salary:
    TextBox	txtDailySalary
    Label		Weekly Salary:
    TextBox	txtWeeklySalary
    Label		Biweekly Salary:
    TextBox	txtBiweeklySalary
    Label		Monthly Salary:
    TextBox	txtMonthlySalary
    Label		Yearly Salary:
    TextBox	txtYearlySalary

20. On the form, double-click the Calculate button
21. Change the document as follows:

    using System;
    using System.Windows.Forms;
    
    namespace SalaryEvaluation2
    {
        public partial class Form1 : Form
        {
            double hourlySalary;
    
            public Form1()
            {
                InitializeComponent();
            }
    
            double EvaluateDailyWages()
            {
                return hourlySalary * 8;
            }
    
            double EvaluateWeeklyWages()
            {
                return hourlySalary * 40;
            }
    
            double EvaluateBiweeklyWages()
            {
                return EvaluateWeeklyWages() * 2;
            }
    
            double EvaluateMonthlyWages()
            {
                return EvaluateWeeklyWages() * 4;
            }
    
            double EvaluateYearlyWages()
            {
                return EvaluateMonthlyWages() * 12;
            }
    
            private void btnCalculate_Click(object sender, EventArgs e)
            {
                hourlySalary = double.Parse(txtHourlySalary.Text);
    
                double dailySalary = EvaluateDailyWages();
                double weeklySalary = EvaluateWeeklyWages();
                double biweeklySalary = EvaluateBiweeklyWages();
                double monthlySalary = EvaluateMonthlyWages();
                double yearlySalary = EvaluateYearlyWages();
    
                txtDailySalary.Text = dailySalary.ToString();
                txtWeeklySalary.Text = weeklySalary.ToString();
                txtBiweeklySalary.Text = biweeklySalary.ToString();
                txtMonthlySalary.Text = monthlySalary.ToString();
                txtYearlySalary.Text = yearlySalary.ToString();
            }
        }
    }

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

    

23. In the Hourly Salary text box, type 22.38
24. Click the Calculate button:

    

25. Close the form and return to your programming environment
26. Remember that you usually declare a variable for the return value of a function if you are planning to use the value (and/or its variable) many times. Otherwise, you may not need the variable, in which case you can call the function directly where you need it. For examples, change the code as follows:

    using System;
    using System.Windows.Forms;
    
    namespace SalaryEvaluation2
    {
        public partial class Form1 : Form
        {
            double hourlySalary;
    
            public Form1()
            {
                InitializeComponent();
            }
    
            . . .
    
            private void btnCalculate_Click(object sender, EventArgs e)
            {
                hourlySalary = double.Parse(txtHourlySalary.Text);
    
                txtDailySalary.Text = EvaluateDailyWages().ToString();
                txtWeeklySalary.Text = EvaluateWeeklyWages().ToString();
                txtBiweeklySalary.Text = EvaluateBiweeklyWages().ToString();
                txtMonthlySalary.Text = EvaluateMonthlyWages().ToString();
                txtYearlySalary.Text = EvaluateYearlyWages().ToString();
                
                // The following line is optional
                return;
            }
        }
    }

A Simple Returning Method With no Body

If you have a function that either contains only one expression or the contents of its body can be resumed to one line, such a function doesn't need a body. Instead, after the parentheses of the function, type => followed by the returning expression.

Practical Learning: Creating a Method without a Body

1. Change the code as follows:

   using System;
   using System.Windows.Forms;
   
   namespace SalaryEvaluation2
   {
       public partial class Form1 : Form
       {
           double hourlySalary;
   
           public Form1()
           {
               InitializeComponent();
           }
   
           double EvaluateDailyWages() => hourlySalary * 8;
   
           double EvaluateWeeklyWages() => hourlySalary * 40;
           
           double EvaluateBiweeklyWages()
           {
               return EvaluateWeeklyWages() * 2;
           }
   
           double EvaluateMonthlyWages()
           {
               return EvaluateWeeklyWages() * 4;
           }
   
           double EvaluateYearlyWages()
           {
               return EvaluateMonthlyWages() * 12;
           }
   
           private void btnCalculate_Click(object sender, EventArgs e)
           {
               hourlySalary = double.Parse(txtHourlySalary.Text);
   
               txtDailySalary.Text = EvaluateDailyWages().ToString();
               txtWeeklySalary.Text = EvaluateWeeklyWages().ToString();
               txtBiweeklySalary.Text = EvaluateBiweeklyWages().ToString();
               txtMonthlySalary.Text = EvaluateMonthlyWages().ToString();
               txtYearlySalary.Text = EvaluateYearlyWages().ToString();
           }
       }
   }

2. To test the project, press Ctrl + F5
3. Close the form and return to your programming environment
4. In the same way, you can call other functions in the returned expression of the one-line function. For examples, change the code as follows:

   using System;
   using System.Windows.Forms;
   
   namespace SalaryEvaluation2
   {
       public partial class Form1 : Form
       {
           double hourlySalary;
   
           public Form1()
           {
               InitializeComponent();
           }
   
           double EvaluateDailyWages() => hourlySalary * 8;
   
           double EvaluateWeeklyWages() => hourlySalary * 40;
           
           double EvaluateBiweeklyWages() => EvaluateWeeklyWages() * 2;
   
           double EvaluateMonthlyWages() => EvaluateWeeklyWages() * 4;
   
           double EvaluateYearlyWages() => EvaluateMonthlyWages() * 12;
   
           private void btnCalculate_Click(object sender, EventArgs e)
           {
               hourlySalary = double.Parse(txtHourlySalary.Text);
   
               txtDailySalary.Text = EvaluateDailyWages().ToString();
               txtWeeklySalary.Text = EvaluateWeeklyWages().ToString();
               txtBiweeklySalary.Text = EvaluateBiweeklyWages().ToString();
               txtMonthlySalary.Text = EvaluateMonthlyWages().ToString();
               txtYearlySalary.Text = EvaluateYearlyWages().ToString();
           }
       }
   }

5. To execute, on the main menu, click Debug -> Start Without Debugging
6. Close the form and return to Microsoft Visual Studio
7. Close Microsoft Visual Studio

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