csharp-basics/2. Variables and Types.md

# Variables & Types

![](imgs/2%20Variables%20and%20Types_0.png)

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# Overview

Variables

Data Types

Arithmetic Operators

Increment & Decrement

Assignment Operators

Strings

Character Constants

String Interpolation

# Variables

* Variable can be thought of as a name for a certain point in computer's memory.
* Using this name we can access the value on the computer's memory
  * We can read the value
  * We can manipulate the value
* On more practical terms: We can assign values to named variables.

# C# Syntax - Declaring Variables

Every variable declaration in C# requires the type and the name of the variable, for example:

int x;

You can assign a value for declared variables:

x = 25;

Variable declaration with value can be executed with one line:

int x = 25;

using System;

namespace MyAwesomeProgram

{

class Program

{

static void Main(string[] args)

{

int a = 25;

int b = 10;

Console.WriteLine(a - b);

}

}

}

Everything within a console application executes inside the Main body

This program prints the value "15" to the console

# Why we use variables?

Variables are key ingredients in programming.

We don't need to know the exact values when we write the code but the values can be given later while the program is executed

As an example we can take an input from a user and store it to a variable and use that value somewhere later in our program

# What is a data type?

* Data type tells to a computer what type of data is stored in a variable.
* Data types are commonly divided into two categories:
  * Primitive data types
  * Reference data types
* Here we go through the primitive data types
  * We dig deeper on the differences of these data types later in the Classes and Objects -section

# Primitive Data Types in C#

| __Type__ | __Represents__ | __Range__ | __Default Value__ |
| :-: | :-: | :-: | :-: |
| __bool__ | __Boolean value__ | __True or False__ | __False__ |
| __byte__ | __8-bit unsigned integer__ | __0 to 255__ | __0__ |
| __char__ | __16-bit Unicode character__ | __U +0000 to U +ffff__ | __\\0'__ |
| __decimal__ | __128-bit precise decimal values with 28-29 significant digits__ | __(-7.9 x 1028 to 7.9 x 1028) / 100 to 28__ | __0.0M__ |
| __double__ | __64-bit double-precision floating point type__ | __(+/-)5.0 x 10-324 to (+/-)1.7 x 10308__ | __0.0D__ |
| __float__ | __32-bit single-precision floating point type__ | __-3.4 x 1038 to + 3.4 x 1038__ | __0.0F__ |
| __int__ | __32-bit signed integer type__ | __-2,147,483,648 to 2,147,483,647__ | __0__ |

More types listed here:

[https://www.w3schools.com/cs/cs\_data\_types.asp](https://www.w3schools.com/cs/cs_data_types.asp)

# Data Types in C# - Example

double airPressure = 1.2;         // Use generally for everything

decimal accountBalance = 1.2m;    // Use for accuracy (e.g. financial applications)

float bulletSpeed = 1.2f;  // Use only when you know the precision will be enough (in other words, don't use)

bool loggedIn = false;

char previousInput = 'b';

# Assignments (variables)

[Assignments about this topic can be found here](https://gitea.buutti.com/education/academy-assignments/src/branch/master/C%23%20Basics/2.1.%20Variables%20&%20Types)

# Assignments (data types)

[Assignments about this topic can be found here](https://gitea.buutti.com/education/academy-assignments/src/branch/master/C%23%20Basics/2.2.%20Data%20Types)

# What are arithmetic operations?

The arithmetic operations are common mathematical operations:

addition

subtraction

multiplication

division

modulus (remainder, in Finnish jakojäännös)

exponentiation

Earlier we used an  _arithmetic operator _ to subtract b from a:

Console.WriteLine(a - b);

# Arithmetic Operators

| Operator | Name | Example | Description |
| :-: | :-: | :-: | :-: |
| + | Addition | a + b | Adds together two values |
| - | Subtraction | a - b | Subtracts one value from another |
| * | Multiplication | a * b | Multiplies two values |
| / | Division | a / b | Divides one value by another |
| % | Modulus | a % b | Returns the division remainder |
| ++ | Increment | a++ | Increases the value of a variable by 1 |
| -- | Decrement | a–- | Decreases the value of a variable by 1 |

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Tässä on kaikki aritmeettiset operaattorit

# Exercise 1: Trying Out Variables

Create a new console application as we did in the last exercise and declare two variables of type  __double__  _._

Assign different values for those variables.

Print the  __sum__ ,  __difference__ ,  __fraction __ and  __product __ of those values to the console.

# Increment & Decrement

Increment and decrement operations are operations that can be used to increment or decrement a variable value by 1.

Most programming languages implement these operations

Addition example:	int a = 3;   a = a + 1;  _// a is now 4_ Can be written with increment:	int a = 3;   a++;  _// a is now 4_

Decrement is like increment but with just subtraction

Substraction example:	int a = 3;   a = a - 1;  _// a is now 2_ Can be written with decrement:	int a = 3;   a--;  _// a is now 2_

Increment and decrement operators can be written in two ways. So sometimes you may also see this:	int a = 3;   --a;  _// a is now 2_  _	_ ++a;  _// a is now 3_

This will do the same thing as a++ and a--. There is a small difference between these syntaxes though.

int a = 3;const _ _ b = _ _ a++;  _// b will be 3_ Console.WriteLine(a);  _// this will print out 4_ Here the assignment to b happens before incrementing a, thus b will be assigned value 3.

int a = 3;const _ _ b = _ _ ++a;  _// b will be 4_ Console.WriteLine(a);  _// this will print out 4_ Here the assignment to b happens after incrementing a, thus b will be assigned value 4.

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Täällä voi helposti demota: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Increment

# Assignment Operators

We have used the assignment operator ' __='__  for assigning values for variables:

int x;

x = 25;

__Notice __ the difference between '=' and the conditional '=='!

'=' is used for assigning values for variables, '== is used for comparing values

| Operator | Example | Same As |
| :-: | :-: | :-: |
| = | x = 5 | x = 5 |
| += | x += 5 | x = x + 5 |
| -= | x -= 5 | x = x - 5 |
| *= | x *= 5 | x = x * 5 |
| /= | x /= 5 | x = x / 5 |
| %= | x %= 5 | x = x % 5 |

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Tässä on joitakin asetusoperaattoreita, lisäksi loogiset (ei käydä tässä)

# Operators - Example

int uppercaseLetters = 2;

uppercaseLetters += 4;          // is now 6

int specialCharacters = 2;

specialCharacters *= 2;         // is now 4

Console.WriteLine(uppercaseLetters);

Console.WriteLine(specialCharacters);

This outputs 6 and 4

# Strings

String is a special type, which contains an array of characters. You can declare and assign strings like any other type of variables:

string name = "Johannes Kantola";

You can concatenate multiple strings with the '+' operator:

string firstName = "Johannes";

string lastName = "Kantola";

string fullName = firstName + " " + lastName;

Console.WriteLine(fullName);    // Outputs "Johannes Kantola"

# Character Constants

Character constants are preceded by a backslash '\\' and can be used for formatting strings

'\\n' represents a newline in the following example:

string firstName = "Johannes";

string lastName = "Kantola";

string fullName = firstName + "\\n" + lastName;

Console.WriteLine(fullName);

/* This outputs

Johannes

Kantola

*/

All character constants: [https://www.tutorialspoint.com/csharp/csharp\_constants.htm](https://www.tutorialspoint.com/csharp/csharp_constants.htm)

# String Interpolation

Concatenating multiple variables into one string with the '+' operator quickly becomes tedious

It's much easier to use  __string interpolation __ by prefixing your target string with '$' and inserting the variables inside curly brackets '{ }':

string animal = "Dog";

string sound = "Woof";

Console.WriteLine($"{animal} says {sound}!");

// Outputs "Dog says Woof!"

# String Formatting

You can add  __format strings__  to change the way variables are interpolated into a string

Add the format string after your variable, separated by a colon (:)

You can find an overview of format strings and a handy list of both standard and custom strings  [here](https://learn.microsoft.com/en-us/dotnet/standard/base-types/formatting-types)

double pi = 3.141592653;

Console.WriteLine($"Pi to three digits: {pi:G3}");

// Outputs "Pi to three digits: 3.14"

# Console.ReadLine()

For the next exercise, you'll need the Console.ReadLine() method. The method pauses the program, waits for an input stream from the console that pops up, and returns the value of the input:

string userInput = Console.ReadLine();Console.WriteLine(userInput);

![](imgs/2%20Variables%20and%20Types_1.png)

# Exercise 2: weekday survey

Create a console application which asks the user which weekday it is and assigns the answer to a string variable.

Print "Have a nice weekday!" to the console where weekday is replaced with the string the user wrote.

# Assignments (arithmetic operations)

[Assignments about this topic can be found here](https://gitea.buutti.com/education/academy-assignments/src/branch/master/C%23%20Basics/2.3.%20Arithmetic%20Operations)