Summary  
This chapter covers input validation using loops combined with try-catch statements to ensure that operator and numeric inputs are correctly parsed before proceeding.  

General domain of usage  
Interactive calculators

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.

This course will give you a solid foundation to begin making applications using .NET in C#. Covering console applications, asynchronous programming, web services, database fundamentals, and ADO.NET CRUD operations, you'll gain practical skills. From creating apps and handling exceptions to optimizing database access, this course ensures a robust understanding of essential .NET development concepts.

In this section we will learn about what is .NET, how to setup the development environment and how to start making some console apps. Apart from that we will also learn how to take input from the user in the console for making interactive applications.

In this section, we will be learning how to perform multiple tasks at once to improve the performance and responsiveness of applications. We will also briefly learn what Web Services and APIs are. This will give us an introduction to how the internet and websites work. We will also learn how to use APIs.

In this section we will learn what are databases, specifically what are SQL databases and how to create them. We will study their structure and will learn to perform some basic operations on the databases. This chapter will serve as an introduction to ADO.NET which is a .NET module used for interacting with databases.

In this section, we'll cover the fundamental CRUD operations (Create, Read, Update, Delete) using SQL. We'll explore SQL syntax at a basic level and recap how to implement each SQL statement in C# code. While some parts may serve as a review from the previous section, this will provide a solid understanding of essential database concepts, enabling you to understand both the SQL and C# code and write it independently.

In this chapter we will learn about additional functions or methods for making database management more efficient. For-example executing multiple SQL commands at once using Stored Procedures, and retrieving data in bulk from the SQL database using DataSet.

Challenge: Improving the Calculator