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Introduction to .NET with C#

Task - Improving the CalculatorTask - Improving the Calculator

The code for the calculator which we created in the previous task is given below. Your task is to add checks to ensure proper user input.

  • Add a check to make sure that the user enters appropriate input for the opr variable. The input should not be empty and should only be equal to +, -, / or *. In case of wrong input, it should prompt the user again for entry. Similar to point 1, add checks for first and second. Make sure the user enters a valid number.

There can be multiple ways to do this. As long as it satisfies the condition, it is a valid solution. Ideally there should be 3 separate try-catch statements for the 3 inputs. You can put all the try-catch statements in a single loop, or separate loops, it is up to your preference.

The TryParse method is not used in these tasks because it is more useful to practice the try-catch statements as they are relevant for the upcoming topics.
Link to the Task: GitHub
Enclose the try-catch check into an infinite while loop and break the loop after the input is successfully parsed. This way you can ensure that the program re-prompts the user in case of wrong input. 

using System;

public class Calculator
{
    public static void Main(string[] args)
    {
        char opr;
        float first, second;

        while (true)
        {
            try
            {
                Console.Write("Enter an operation (+, -, /, *): ");
                opr = Console.ReadLine()[0];

                // 'Contains' method checks if a string contains a character or a substring.
                if ("/-+*".Contains(opr))
                    break;

            }
            catch { }
            Console.WriteLine("The operator is invalid.");
        }

        while (true)
        {
            try
            {
                Console.Write("Enter the first number: ");
                first = float.Parse(Console.ReadLine());
                break;
            }
            catch
            {
                Console.WriteLine("The first number is invalid. ");
            }
        }

        while (true)
        {
            try
            {
                Console.Write("Enter the second number: ");
                second = float.Parse(Console.ReadLine());
                break;
            }
            catch
            {
                Console.WriteLine("The second number is invalid. ");
            }
        }


        float result = 0;
        if (opr == '+')
            result = first + second;
        else if (opr == '-')
            result = first - second;
        else if (opr == '/')
            result = first / second;
        else if (opr == '*')
            result = first * second;

        Console.WriteLine($"The result of '{first} {opr} {second}' is: {result}");
    }
}

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Секція 1. Розділ 6
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Зміст курсу

Introduction to .NET with C#

1. Introduction

What is the .NET Platform exactly?Creating a Console ApplicationTaking input from the UserTask - Building a Simple CalculatorDealing with Exceptions caused by User InputTask - Improving the CalculatorReading FilesWriting FilesTask - File Based Calculator

2. Asynchronous Programming and Introduction to Web Services

What is Asynchronous Programming?Implementing an Asynchronous MethodTask - Asynchronously Reading FilesIntroduction to APIsMaking a GET RequestTask - Using an APIHandling Exceptions caused by HTTP RequestTask - Exception Handling for API Response

3. Introduction to Databases with .NET

What is a Database?Structure of a Relational DatabaseSetting Up A MySQL ServerConnecting to the MySQL ServerTask - Writing Connection StringsExecuting CommandsTask - Executing MySQL CommandsMySqlCommand MethodsTask - Connecting to a MySQL Database and Executing Commands

4. CRUD Operations with MySQL

Introduction to CRUD OperationsInstalling & Using MySQL WorkbenchCREATE - Part ITask - Using CREATECREATE - Part IITask - Using INSERTReadTask - Using SELECTUpdateTask - Using UPDATEDelete - Part IDelete - Part IITask - Using DELETE

5. Optimizing Database Operations

Stored ProceduresTask - Executing Stored ProceduresDataReader vs DataSetDataAdapter & DataSetTask - Reading Tables using MySqlDataAdapterWhat's Next?

Introduction to .NET with C#

Task - Improving the CalculatorTask - Improving the Calculator

The code for the calculator which we created in the previous task is given below. Your task is to add checks to ensure proper user input.

  • Add a check to make sure that the user enters appropriate input for the opr variable. The input should not be empty and should only be equal to +, -, / or *. In case of wrong input, it should prompt the user again for entry. Similar to point 1, add checks for first and second. Make sure the user enters a valid number.

There can be multiple ways to do this. As long as it satisfies the condition, it is a valid solution. Ideally there should be 3 separate try-catch statements for the 3 inputs. You can put all the try-catch statements in a single loop, or separate loops, it is up to your preference.

The TryParse method is not used in these tasks because it is more useful to practice the try-catch statements as they are relevant for the upcoming topics.
Link to the Task: GitHub
Enclose the try-catch check into an infinite while loop and break the loop after the input is successfully parsed. This way you can ensure that the program re-prompts the user in case of wrong input. 

using System;

public class Calculator
{
    public static void Main(string[] args)
    {
        char opr;
        float first, second;

        while (true)
        {
            try
            {
                Console.Write("Enter an operation (+, -, /, *): ");
                opr = Console.ReadLine()[0];

                // 'Contains' method checks if a string contains a character or a substring.
                if ("/-+*".Contains(opr))
                    break;

            }
            catch { }
            Console.WriteLine("The operator is invalid.");
        }

        while (true)
        {
            try
            {
                Console.Write("Enter the first number: ");
                first = float.Parse(Console.ReadLine());
                break;
            }
            catch
            {
                Console.WriteLine("The first number is invalid. ");
            }
        }

        while (true)
        {
            try
            {
                Console.Write("Enter the second number: ");
                second = float.Parse(Console.ReadLine());
                break;
            }
            catch
            {
                Console.WriteLine("The second number is invalid. ");
            }
        }


        float result = 0;
        if (opr == '+')
            result = first + second;
        else if (opr == '-')
            result = first - second;
        else if (opr == '/')
            result = first / second;
        else if (opr == '*')
            result = first * second;

        Console.WriteLine($"The result of '{first} {opr} {second}' is: {result}");
    }
}

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Секція 1. Розділ 6
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