theme: Next, 1

[fit] Computers

... are machines that accept input, manipulate data, and produce output.

[fit] Variable

... is an identifier for a value our program needs to keep track of

                                 +------------------------------------------------------------------+
                                 |                           COMPUTER MEMORY                        |
                                 |                                                                  |
                                 |                                                                  |
                                 |                                                                  |
                                 |               +---------------------------------------+          |
                                 |               |                                       |          |
                                 |               |                                       |          |
                                 |               |    "Suncoast Developers Guild"        |          |
myVariable  +------------------------------------+                                       |          |
                                 |               |                                       |          |
                                 |               +---------------------------------------+          |
                                 |                                                                  |
                                 |                                                                  |
                                 |          +-------+                                               |
                                 |          |       |                                               |
 myOtherVariable  +-----------------------> |  42   |                                               |
                                 |          |       |                                               |
                                 |          +-------+                                               |
                                 |                                                                  |
                                 |                                                                  |
                                 |                                                                  |
                                 |                                                                  |
                                 |                                                                  |
                                 +------------------------------------------------------------------+

Language Rules

• Naming variables
• The kinds (types) of information we can store in variables
• If the value of a variable, once assigned, can be changed
• The syntax for declaring a variable
• If the kind (type) of information stored in a variable can change once assigned

C# rules

• Must declare our variables before we can use them.
• Must tell C# what kind of information the variable will store.
• From our example myVariable stores a series of letters and spaces and myOtherVariable stores a number.
• These represent the variables type.

Our first C# types

• A sequence of letters, numbers, digits, emoji _🚀, spaces, etc. is called a string
• A whole number (without any decimal places) is called an int (short for integer)

How do you make a variable?

string name = "Samantha";
int score = 95;

Break it down

[.code-highlight: 1]

string name = "Samantha";
int score = 95;

Breaking it down

// Type   Name   Value    Statement End
//  |       |      |       |
//  |       |      |       |
//  v       v      v       v
  string  name = "Samantha";

^ Assignment Statement ^ Left Side vs Right Side ^ Double quotes for strings ^ ; in C# is like the period at the end of a sentence

Break it down

[.code-highlight: 2]

string name = "Samantha";
int score = 95;

// Type   Name   Value    Statement End
//  |       |      |       |
//  |       |      |       |
//  v       v      v       v
   int    score = 95;

^ No double quotes for int

Let C# do the work

• Programmers like to be efficient _{Some might say lazy}
• Let the computer do the work when we can
  
  
• Type inference _{Let C# figure out what to write where type goes.}

Type Inference

var name = "Samantha";
var score = 95;

• var keyword allows C# to automatically_{automagically?} determine the type of variable based on the value on the right hand side.
  
• This is how we will create variables most of the time.

^ We will use type inference almost always when declaring variables. There will be cases where we cannot.

So what else ya got?

• Numeric primitive types
• Non-numeric primitive types
• Reference types

^ Reference types store data that can have wide ranges of values

Numeric types

[.autoscale: true]

• int : a whole number from -2,147,483,648 to 2,147,483,647
• long : a whole number from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
• double : a 64 bit floating point value that has an approximate precision of ~15-17 digits
• float : a 32 bit floating point value that has an approximate precision of 6-9 digits
• decimal : a more precise way to store decimal numbers, but has a smaller range

^ Don't memorize these, just know they exist.

Non-numeric primitive types

• char : represents a unicode character, a single letter, or an emoji. This is what strings are made of.
• bool : true or false
• byte : represents a raw chunk of data (values from 0 to 255)

Examples

[.column]

Integers

var score = 42;

Double

var total = 10.0;
var alsoTotal = 10d;
var pi = 3.14159265;

[.column]

Floats

var total = 10f;
var price = 10.0f;
var pi = 3.14159265f;

Decimal

var total = 10m;
var price = 10.0m;
var pi = 3.14159265m;

Examples

[.column]

Characters

var piratesFavoriteLetter = 'r';
var firstLetterOfTheEnglishAlphabet = 'a';
var lastLetterOfTheEnglishAlphabet = 'z';
var capitalLetter = 'Q';
var rocketShip = '🚀';

Strings

var name = "Zaphod Beeblebrox";

[.column]

Boolean

var theCakeIsALie = true;
var worldIsFlat = false;

Math

Addition, subtraction, multiplication, division, remainder (modulus)

var firstNumber = 42;
var secondNumber = 12;
var sum = firstNumber + secondNumber;
var difference = secondNumber - firstNumber;
var product = firstNumber * secondNumber;
var division = firstNumber / secondNumber;
var remainder = firstNumber % secondNumber;

PEMDAS

PEMDAS

var answer = 2 + 3 * 4; // 14
var answer2 = (2 + 3) * 4; // 20

NOTE: There are other order of operations in code. We may see some of those later.

Strings have extra features!

More complex types, like string can be asked questions about itself.

How long is a string?

[.code-highlight: 2]

var sentence = "The quick brown fox jumped over the lazy dog";
var howLong = sentence.Length;

^ Variable being used on the right hand side for the first time. ^ Right side first ^ Result goes into variable on the left side ^ The . in the sentence.Length asks the variable sentence for its Length property.

Break it down

[.column]

//     variable  right-hand-side
//        |             |
//        v             v
    var howLong = sentence.Length;

[.column]

// variable  property
//    |         |
//    v         v
    sentence.Length

^ Computer first goes to the contents of the variable (sentence) in memory and then looks at the property Length and it figures out what that property value is. ^ In this case the int 44.

Results

var sentence = "The quick brown fox jumped over the lazy dog";
var howLong = sentence.Length;

The howLong variable will know it is an int, and its contents will be 44

[.autoscale: true]

DateTime

C# comes with a specialized class to deal with storing a date and time.

A DateTime is a Year, Month, Day, Hour, Minute, Second, and Millisecond.

To create a DateTime variable equal to the current time you can use this syntax:

var rightNow = DateTime.Now

If you then wanted to know the current month:

var rightNow = DateTime.Now;
var currentMonth = rightNow.Month;

About naming variables

• Use clear variable names.
• Longer variable names don't cost anything.
• Remember that code is written once but read many times.
• You may be the one reading it later.

Always code as if the developer who ends up maintaining your code knows where you live. Code for readability. -- A wise developer

[.column]

Not good

var w = 52;
var n = "Arthur Dent";
var i = 1;
var resp = axios.get();

[.column]

Better

var weeksInOneYear = 52;
var name = "Arthur Dent";
var currentDepartmentIndex = 1;
var response = axios.get();

^ Follow the pattern of your team. On the SDG team we are going to use descriptive variable names and avoid one letter variables and abbreviations.