# Chapter 2.1. Simple Calculations

In this chapter we are going to get familiar with the following concepts and programming techniques:

• What is the system console?
• How to read numbers from the system console?
• How to work with data types and variables, which are necessary to process numbers and the operations between them?
• How to print output (a number) on the console?
• How to do simple arithmetic operations: add, subtract, multiply, divide, string concatenation?

## Video: Chapter Overview

Watch a video lesson about what shall we learn in this chapter here: https://youtu.be/NXbFJw_NstA.

## Introduction to Simple Calculations by Examples

Computer programs can enter data from the console, perform calculations and print the results on the console. This is a simple example of C# program that converts from foots to meters:

Console.Write("Foots = ");
var meters = foots * 0.3048;
Console.Write("Meters = ");
Console.WriteLine(meters);


Run the above code example: https://repl.it/@nakov/foots-to-meters-csharp.

The above program enters a number and converts its value from foots to meters. This is a sample output from the above code, when the user enters 5 as input:

Foots = 5
Meters = 1.524


In C# we can read a text line from the console using Console.ReadLine() and we can convert the text to a floating-point number using double.Parse(text). We can print text and numbers using the $text formatting syntax as follows: var radius = 1.25; Console.WriteLine($"Circle radius = {radius}");
Console.WriteLine($"Circle area = {Math.PI * radius * radius}");  Run the above code example: https://repl.it/@nakov/circle-area-csharp. The$ syntax replaces all expressions in curly brackets with their values. The output from the above code is:

Circle radius = 1.25
Circle area = 4.90873852123405


Let's explain in greater detail how to use the console, how to enter numbers and text and how to perform simple calculations and format and print text and expressions on the console in C#.