Tutorials

Tutorial: Create a simple C# console app in Visual Studio

  • 10 minutes to read
  • Contributors
    • Terry G. Lee
      •  
    • Genevieve Warren
      •  
    • PRMerger6
      •  
    • Mike Jones
      •  
    • Terry G. Lee
      •  
    • all
In this tutorial for C#, you'll use Visual Studio to create and run a console app and explore some features of the Visual Studio integrated development environment (IDE) while you do so.
If you haven't already installed Visual Studio, go to the Visual Studio downloads page to install it for free.

Create a project

To start, we'll create a C# application project. The project type comes with all the template files you'll need, before you've even added anything!
  1. Open Visual Studio 2017.
  2. From the top menu bar, choose File > New > Project.
  3. In the New Project dialog box in the left pane, expand C#, and then choose .NET Core. In the middle pane, choose Console App (.NET Core). Then name the file Calculator.
    Console App (.NET Core) project template in the New Project dialog box in the Visual Studio IDE

Add a workload (optional)

If you don't see the Console App (.NET Core) project template, you can get it by adding the .NET Core cross-platform development workload. Here's how.

Option 1: Use the New Project dialog box

  1. Choose the Open Visual Studio Installer link in the left pane of the New Project dialog box.
    Choose the Open Visual Studio Installer link from the New Project dialog box
  2. The Visual Studio Installer launches. Choose the .NET Core cross-platform developmentworkload, and then choose Modify.
    .NET Core cross-platform development workload in the Visual Studio Installer

Option 2: Use the Tools menu bar

  1. Cancel out of the New Project dialog box and from the top menu bar, choose Tools > Get Tools and Features.
  2. The Visual Studio Installer launches. Choose the .NET Core cross-platform developmentworkload, and then choose Modify.

Create the app

First, we'll explore some basic integer math in C#. Then, we'll add code to create a basic calculator. Next, we'll tweak the code to add functionality. After that, we'll debug the app to find and fix errors. And finally, we'll refine the code to make it more efficient.
Let's start with some integer math in C#.
  1. In the code editor, delete the default "Hello World" code.
    Delete the default Hello World code from your new calculator app
    Specifically, delete the line that says, Console.WriteLine("Hello World!");.
  2. In its place, type the following code:
            int a = 42;
        int b = 119;
        int c = a + b;
        Console.WriteLine(c);
        Console.ReadKey();
  3. Choose Calculator to run your program, or press F5.
    Choose the Calculator button to run the app from the toolbar
    A console window opens that reveals the sum of 42 + 119.
  4. Now try changing the int c = a + b; line of code by using a different operator, such as - for subtraction, * for multiplication, or / for division.
    Notice that when you change the operator and run the program, the result changes, too.
Let's continue by adding a more complex set of calculator code to your project.
  1. Delete all the code you see in the code editor.
  2. Enter or paste the following new code into the code editor:
    using System;

namespace Calculator
{
    class Program
    {
        static void Main(string[] args)
        {
            // Declare variables and then initialize to zero
            int num1 = 0; int num2 = 0;

            // Display title as the C# console calculator app
            Console.WriteLine("Console Calculator in C#\r");
            Console.WriteLine("------------------------\n");

            // Ask the user to type the first number
            Console.WriteLine("Type a number, and then press Enter");
            num1 = Convert.ToInt32(Console.ReadLine());

            // Ask the user to type the second number
            Console.WriteLine("Type another number, and then press Enter");
            num2 = Convert.ToInt32(Console.ReadLine());

            // Ask the user to choose an option
            Console.WriteLine("Choose an option from the following list:");
            Console.WriteLine("\ta - Add");
            Console.WriteLine("\ts - Subtract");
            Console.WriteLine("\tm - Multiply");
            Console.WriteLine("\td - Divide");
            Console.Write("Your option? ");

            // Use a switch statement to do the math
            switch (Console.ReadLine())
            {
                case "a":
                    Console.WriteLine($"Your result: {num1} + {num2} = " + (num1 + num2));
                    break;
                case "s":
                    Console.WriteLine($"Your result: {num1} - {num2} = " + (num1 - num2));
                    break;
                case "m":
                    Console.WriteLine($"Your result: {num1} * {num2} = " + (num1 * num2));
                    break;
                case "d":
                    Console.WriteLine($"Your result: {num1} / {num2} = " + (num1 / num2));
                    break;
            }
            // Wait for the user to respond before closing
            Console.Write("Press any key to close the Calculator console app...");
            Console.ReadKey();
        }
    }
}
  3. Choose Calculator to run your program, or press F5.
    Choose the Calculator button to run the app from the toolbar
    A console window opens.
  4. View your app in the console window, and then follow the prompts to add the numbers 42 and 119.
    Your app should look similar to the following screenshot:
    Console window showing the Calculator app and includes prompts on which actions to take

Add decimals

The calculator app currently accepts and returns whole numbers. But, it'll be more precise if we add code that allows for decimals.
As in the following screenshot, if you run the app and divide number 42 by the number 119, your result is 0 (zero), which isn't exact.
Console window showing the Calculator app that doesn't return a decimal numeral as a result
Let's fix the code so that it handles decimals.
  1. Press Ctrl + F to open the Find and Replace control.
  2. Change each instance of the int variable to float.
    Animation of the Find and Replace control showing how to change the int variable to float
  3. Run your calculator app again and divide the number 42 by the number 119.
    Notice that the app now returns a decimal numeral instead of zero.
    Console window showing the Calculator app that now returns a decimal numeral as a result
However, the app produces only a decimal result. Let's make a few more tweaks to the code so that the app can calculate decimals too.
  1. Use the Find and Replace control (Ctrl + F) to change each instance of the floatvariable to double, and to change each instance of the Convert.ToInt32 method to Convert.ToDouble.
  2. Run your calculator app and divide the number 42.5 by the number 119.75.
    Notice that the app now accepts decimal values and returns a longer decimal numeral as its result.
    Console window showing the Calculator app that now accepts decimal numbers and returns a longer decimal numeral as a result
    (We'll fix the number of decimal places in the Revise the code section.)

Debug the app

We've improved on our basic calculator app, but it doesn't yet have failsafes in place to handle exceptions, such as user input errors.
For example, if you try to divide a number by zero, or enter an alpha character when the app expects a numeric character (or vice versa), the app stops working and returns an error.
Let's walk through a few common user input errors, locate them in the debugger, and fix them in the code.
Tip
For more information about the debugger and how it works, see the First look at the Visual Studio debugger page.

Fix the "divide by zero" error

When you try to divide a number by zero, the console app freezes. Visual Studio then shows you what's wrong in the code editor.
The Visual Studio code editor shows the divide-by-zero error
Let's change the code to handle this error.
  1. Delete the code that appears directly between case "d": and the comment that says // Wait for the user to respond before closing.
  2. Replace it with the following code:
             // Ask the user to enter a non-zero divisor until they do so
             while (num2 == 0)
             {
                 Console.WriteLine("Enter a non-zero divisor: ");
                 num2 = Convert.ToInt32(Console.ReadLine());
             }
             Console.WriteLine($"Your result: {num1} / {num2} = " + (num1 / num2));
             break;
     }
    After you add the code, the section with the switch statement should look similar to the following screenshot:
    The revised "switch" section in the Visual Studio code editor
Now, when you divide any number by zero, the app will ask for another number. Even better: It won't stop asking until you provide a number other than zero.
The Visual Studio code editor shows the divide-by-zero error

Fix the "format" error

If you enter an alpha character when the app expects a numeric character (or vice versa), the console app freezes. Visual Studio then shows you what's wrong in the code editor.
The Visual Studio code editor shows a format error
To fix this error, we must refactor the code that we've previously entered.

Revise the code

Rather than rely on the program class to handle all the code, we'll divide our app into two classes: calculator and program.
The calculator class will handle the bulk of the calculation work, and the program class will handle the user interface and error-capturing work.
Let's get started.
  1. Delete everything after the following code block:
    
using System;

namespace Calculator
{
  2. Next, add a new calculator class, as follows:
    class Calculator
{
    public static double DoOperation(double num1, double num2, string op)
    {
        double result = double.NaN; // Default value is "not-a-number" which we use if an operation, such as division, could result in an error

        // Use a switch statement to do the math
        switch (op)
        {
            case "a":
                result = num1 + num2;
                break;
            case "s":
                result = num1 - num2;
                break;
            case "m":
                result = num1 * num2;
                break;
            case "d":
                // Ask the user to enter a non-zero divisor
                if (num2 != 0)
                {
                    result = num1 / num2;
                }
                break;
            // Return text for an incorrect option entry
            default:
                break;
        }
        return result;
    }
}
  3. Then, add a new program class, as follows:
    class Program
{
    static void Main(string[] args)
    {
        bool endApp = false;
        // Display title as the C# console calculator app
        Console.WriteLine("Console Calculator in C#\r");
        Console.WriteLine("------------------------\n");

        while (!endApp)
        {
            // Declare variables and set to empty
            string numInput1 = "";
            string numInput2 = "";
            double result = 0;

            // Ask the user to type the first number
            Console.Write("Type a number, and then press Enter: ");
            numInput1 = Console.ReadLine();

            double cleanNum1 = 0;
            while (!double.TryParse(numInput1, out cleanNum1))
            {
                Console.Write("This is not valid input. Please enter an integer value: ");
                numInput1 = Console.ReadLine();
            }

            // Ask the user to type the second number
            Console.Write("Type another number, and then press Enter: ");
            numInput2 = Console.ReadLine();

            double cleanNum2 = 0;
            while (!double.TryParse(numInput2, out cleanNum2))
            {
                Console.Write("This is not valid input. Please enter an integer value: ");
                numInput2 = Console.ReadLine();
            }

            // Ask the user to choose an operator
            Console.WriteLine("Choose an operator from the following list:");
            Console.WriteLine("\ta - Add");
            Console.WriteLine("\ts - Subtract");
            Console.WriteLine("\tm - Multiply");
            Console.WriteLine("\td - Divide");
            Console.Write("Your option? ");

            string op = Console.ReadLine();

            try
            {
                result = Calculator.DoOperation(cleanNum1, cleanNum2, op);
                if (double.IsNaN(result))
                {
                    Console.WriteLine("This operation will result in a mathematical error.\n");
                }
                else Console.WriteLine("Your result: {0:0.##}\n", result);
            }
            catch (Exception e)
            {
                Console.WriteLine("Oh no! An exception occurred trying to do the math.\n - Details: " + e.Message);
            }

            Console.WriteLine("------------------------\n");

            // Wait for the user to respond before closing
            Console.Write("Press 'n' and Enter to close the app, or press any other key and Enter to continue: ");
            if (Console.ReadLine() == "n") endApp = true;

            Console.WriteLine("\n"); // Friendly linespacing
        }
        return;
    }
}
  4. Choose Calculator to run your program, or press F5.
  5. Follow the prompts and divide the number 42 by the number 119. Your app should look similar to the following:
    Console window showing the refactored Calculator app that includes prompts on which actions to take and error handling for incorrect inputs
    Notice that you have the option to enter more equations until you choose to close the console app. And, we've also reduced the number of decimal places in the result.

Close the app

  1. If you haven't already done so, close the calculator app.
  2. Close the Output pane in Visual Studio.
    Close the Output pane in Visual Studio
  3. In Visual Studio, press Ctrl+S to save your app.
  4. Close Visual Studio.

Code complete

During this tutorial, we've made a lot of changes to the calculator app. The app now handles computing resources more efficiently, and it handles most user input errors.
Here's the complete code, all in one place:

using System;

namespace Calculator
{
    class Calculator
    {
        public static double DoOperation(double num1, double num2, string op)
        {
            double result = double.NaN; // Default value is "not-a-number" which we use if an operation, such as division, could result in an error

            // Use a switch statement to do the math
            switch (op)
            {
                case "a":
                    result = num1 + num2;
                    break;
                case "s":
                    result = num1 - num2;
                    break;
                case "m":
                    result = num1 * num2;
                    break;
                case "d":
                    // Ask the user to enter a non-zero divisor
                    if (num2 != 0)
                    {
                        result = num1 / num2;
                    }
                    break;
                // Return text for an incorrect option entry
                default:
                    break;
            }
            return result;
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            bool endApp = false;
            // Display title as the C# console calculator app
            Console.WriteLine("Console Calculator in C#\r");
            Console.WriteLine("------------------------\n");

            while (!endApp)
            {
                // Declare variables and set to empty
                string numInput1 = "";
                string numInput2 = "";
                double result = 0;

                // Ask the user to type the first number
                Console.Write("Type a number, and then press Enter: ");
                numInput1 = Console.ReadLine();

                double cleanNum1 = 0;
                while (!double.TryParse(numInput1, out cleanNum1))
                {
                    Console.Write("This is not valid input. Please enter an integer value: ");
                    numInput1 = Console.ReadLine();
                }

                // Ask the user to type the second number
                Console.Write("Type another number, and then press Enter: ");
                numInput2 = Console.ReadLine();

                double cleanNum2 = 0;
                while (!double.TryParse(numInput2, out cleanNum2))
                {
                    Console.Write("This is not valid input. Please enter an integer value: ");
                    numInput2 = Console.ReadLine();
                }

                // Ask the user to choose an operator
                Console.WriteLine("Choose an operator from the following list:");
                Console.WriteLine("\ta - Add");
                Console.WriteLine("\ts - Subtract");
                Console.WriteLine("\tm - Multiply");
                Console.WriteLine("\td - Divide");
                Console.Write("Your option? ");

                string op = Console.ReadLine();

                try
                {
                    result = Calculator.DoOperation(cleanNum1, cleanNum2, op);
                    if (double.IsNaN(result))
                    {
                        Console.WriteLine("This operation will result in a mathematical error.\n");
                    }
                    else Console.WriteLine("Your result: {0:0.##}\n", result);
                }
                catch (Exception e)
                {
                    Console.WriteLine("Oh no! An exception occurred trying to do the math.\n - Details: " + e.Message);
                }

                Console.WriteLine("------------------------\n");

                // Wait for the user to respond before closing
                Console.Write("Press 'n' and Enter to close the app, or press any other key and Enter to continue: ");
                if (Console.ReadLine() == "n") endApp = true;

                Console.WriteLine("\n"); // Friendly linespacing
            }
            return;
        }
    }
}

1 comment:

  1. MisgeMarch 27, 2019 at 6:19 AM

    great explanation for beginner respect kb
    betam des yilal
    des ylal

    ReplyDelete

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