Initial commit for public repo

code/arithmetic.php

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+<?php
+
+// Now that we know how to create variables, let's look at doing some math.
+$a = 1;
+$b = 2;
+
+// To add two values, use the plus symbol.
+$c = $a + $b;
+
+// To subtract, use the minus symbol.
+$c = $b - $a;
+
+// To multiply two values, use an asterisk.
+echo $a * $b;
+
+// To divide values, use a forward slash.
+echo $b / $a;
+
+// PHP uses the percent symbol for calculating the modulus of two numbers.
+// The modulus is calculated by dividing two numbers and returning the remainder of the result.
+// So, in this example, the value of $modulo will be 0.
+$modulo = 10 % 5;
+
+// You can also use double asterisks to calculate a number to the power of another number.
+// The following statement will print 25.
+echo 5 ** 2;

code/arrays.php

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+<?php
+
+// There are two ways to create an array.
+// First, you can use the array construct to pass in values separated by commas
+// and it will return an array.
+$taskList = array('grocery store', 'change car oil');
+
+// Second, you can surround the list in square brackets.
+// This style is the most common and recommended form
+// of creating an array.
+$groceryList = ['bread', 'milk', 'eggs'];
+
+// PHP will automatically assign index keys for each value in an array
+// starting with 0. So, to access a value in an array you will
+// pass the key number into brackets after the variable name.
+echo $groceryList[0] . "\n";
+echo $groceryList[1] . "\n";
+
+// You can also assign keys in an array using numbers or strings.
+// It is very common to create an array with string keys. The pattern
+// is called an associative array or a map.
+$car = ['make' => 'Toyota', 'model' => 'Camry'];
+
+// To access the value in an associative array, just use the string key in brackets
+// after the variable name.
+echo $car['model'] . "\n";

code/basics.php

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+<?php
+
+// In the tradition of our ancestors, let's start with a hello world program.
+// All PHP files must start with a <?php tag unless it is for a html template.
+// (We will learn about html templates later.)
+echo "Hello World!\n";
+
+// There is a lot going on in this statement so let's work through it.
+
+// First, the echo keyword tells PHP to output some text.
+echo 'I am some text';
+
+// Second, PHP stores text in strings.
+
+// To write a string, you surround letters with single or double quotes.
+// The difference between single quoted strings and double quoted strings
+// is that double quoted strings can hold special characters like \n which tells PHP to start a new line.
+'I am a string';
+"\nI am a string on a new line";
+
+// Third, all lines of code in PHP must end in a semi-colon.
+echo "No semi-colon is a no-no\n";
+
+// Using semi-colons means we can write multiple statements on one line.
+echo 'Hello'; echo " World\n";

code/boolean-logic.php

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+<?php
+
+// Boolean logic is used to combine booleans to return another boolean.
+
+// Using double ampersands tells PHP to check if both values are true.
+// If so, it will return true. If not, it will return false.
+$a = true;
+$b = true;
+$c = false;
+
+// Returns true.
+$a && $b;
+// Returns false.
+$a && $c;
+
+// Using two pipe characters checks if either value is true.
+// Then, it will return true. If both values are false, the PHP
+// returns false.
+$a = true;
+$b = false;
+$c = false;
+$d = true;
+
+// Returns true.
+$a || $b;
+// Returns false.
+$b || $c;
+// Returns true.
+$a || $d;
+
+// Using an exclamation point returns the value flipped.
+$d = true;
+
+// Outputs false.
+echo !$d;

code/classes.php

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+<?php
+
+// Classes allow you to define your own data types. All classes start with the
+// class keyword followed by the name of the class and opening and closing curly braces.
+class Car
+{
+}
+
+// To create an instance of a class, you use the "new" keyword in front of the class name
+// with parentheses.
+$car = new Car();
+
+// A class can define attributes and methods. An attribute is a piece of data
+// stored on the class instance. You can define an attribute by adding the
+// word "public" and a variable name inside the class definition.
+class Bicycle
+{
+    public $color;
+}
+
+// Then, when you create an instance of the class, you can set and use
+// the color attribute on the bicycle using "->".
+$bike = new Bicycle();
+$bike->color = 'Blue';
+echo $bike->color . "\n";
+
+// A method is a function attached to the class. You can add a method
+// to a class by using the "public" keyword followed by the function. A method
+// can access the attributes and methods of the instance using the "$this" variable.
+class Tricycle
+{
+    public $color;
+
+    public function echoColor()
+    {
+        echo $this->color . "\n";
+    }
+}
+
+$bike = new Tricycle();
+$bike->color = 'Red';
+$bike->echoColor();

code/comparisons.php

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+<?php
+
+// A boolean is a value that is always 0 or 1, yes or no, on or off.
+// In PHP, a boolean is represented by the words true and false.
+// While programming, you will often want to know if something is true or false.
+$a = true;
+$b = false;
+
+// There are many constructs and functions that will return a boolean.
+// To start, let's look at comparisons.
+$one = 1;
+$two = 2;
+
+// Double equals checks if two values are equal.
+// This statement will return false.
+$one == $two;
+
+// An exclamation point and equal sign check if two values are not equal.
+// This statement will return true.
+$one != $two;
+
+// You can use greater than and less than symbols to check for comparisons too.
+// This statement will return false.
+$one > $two;
+
+// This statement will return true.
+$one < $two;
+
+// If you combine a greater than or less than symbol with an equal,
+// it will check if the value is greater or less than or equal to another value.
+$one <= $two;
+$one >= $two;
+
+// You can also check that two values are equal and of the same type
+// by using three equal signs.
+
+// This returns true.
+1 == '1';
+
+// This returns false.
+1 === '1';

code/conditionals.php

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+<?php
+
+// When writing code, there will be times when you need to perform actions only under certain circumstances.
+// There are several ways to control execution in PHP.
+// We will start with an if statement.
+$animal = 'cow';
+if ($animal == 'cow') {
+    echo "Moooooo.....\n";
+}
+
+// All conditionals check to see if a statement evaluates to true or false.
+// In the case above, since $animal equals 'cow', the statement returns true and the contents of the if statement are executed.
+
+
+// An if statement can have multiple conditions chained together.
+// If the first if statement returns false, then PHP will check each elseif.
+// If none of the checks return true, then the else block will be executed.
+$animal = 'bird';
+if ($animal == 'dog') {
+    echo "Woof! 🐶\n";
+} elseif ($animal == 'cat') {
+    echo "Meow!? 🐱\n";
+} elseif ($animal == 'bird') {
+    echo "Chirp! 🐦\n";
+} else {
+    echo "I am not a dog, cat or bird\n";
+}
+
+// An alternative to the if statement is the switch.
+// A switch statement has multiple cases  to check if the value in parentheses equals something.
+// In this statement, since $food equals 'apples', the switch will echo "Eating an apple".
+// The default case will be run if no other case evaluates to true, like an else statement.
+$food = 'apples';
+switch ($food) {
+    case 'apples':
+        echo "Eating an apple\n";
+        break;
+    case 'oranges':
+        echo "Eating an orange\n";
+        break;
+    case 'peaches':
+        echo "Eating a peach\n";
+        break;
+    default:
+        echo "No food, I am hungry\n";
+}
+
+// Breaks are a special keyword that tell PHP to stop execution once a case passes.
+// If you do not use a break, PHP will continue to execute all following cases.
+// In this switch, both "Drinking water" and "Drinking tea" will be executed since there is no break in the 'water' case.
+$drink = 'water';
+switch ($drink) {
+    case 'water':
+        echo "Drinking water\n";
+    case 'tea':
+        echo "Drinking tea\n";
+        break;
+}
+
+// PHP also supports single line conditionals called a ternary.
+// In a ternary, the condition is followed by a question mark before the value that should be returned if the condition is true and then another colon and a value to return if the condition is false.
+$language = 'english';
+echo $language == 'spanish' ? "hola\n" : "hello\n";
+
+// Lastly, there is another form of a ternary that checks if a value is set and then returns the value to the right of two question marks if value is null.
+echo $IDoNotExist ?? "Variable not set\n";
+
+// You can also chain multiple checks in a row.
+$IExist = "Variable exists\n";
+echo $IDoNotExist ?? $IExist ?? "Neither variable is set\n";

code/functions.php

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+<?php
+
+// A function allows you to store code under a name and then execute
+// that code later.
+
+// A function always starts with the
+// function keyword followed by the name with parentheses and then
+// opening and closing curly braces around the code.
+function hello_world() {
+    echo "hello world\n";
+}
+
+// To call the function, use the function name with parentheses.
+hello_world();
+
+// You can set up values to be passed into a function.
+// To do so, write variables in between the function parentheses.
+// Each one should be separated by a comma.
+function greet($firstname, $lastname) {
+    echo "hello $firstname $lastname\n";
+}
+
+// Then, you can pass in values when calling a function. In the greet function,
+// 'John' is assigned to $firstname and 'Smith' is assigned to
+// $lastname.
+greet('John', 'Smith');
+
+// You can also return a value from a function. You can only
+// return a single value from a function.
+function capitalize($value) {
+    return strtoupper($value);
+}
+
+// When calling a function, it will output the return value which
+// you can load into a variable.
+$animal = capitalize('dog');
+echo "$animal\n";
+
+// You can also create nameless functions called closures. Closures can be
+// stored in variables or passed into other functions.
+$sum = function ($a, $b) {
+    return $a + $b;
+};
+
+// You can execute a closure by putting parentheses after the variable.
+echo $sum(1, 2) . "\n";

code/loops.php

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+<?php
+
+// A loop tells PHP to run a block of code more than once.
+// A classic loop is a while loop.
+// A "while" loop will continue to run the block of code as long as the value in parentheses is true.
+$num = 5;
+while ($num > 0) {
+    echo "While loop $num\n";
+    --$num;
+}
+
+// A "do while" loop is similar to a "while" loop except it always runs at least
+// one iteration. In a classic "while" loop, no iterations may be executed if
+// the value in parentheses is false. In a "do while", the boolean check
+// is not done until after the execution of an iteration.
+$num = 0;
+do {
+    echo "Do while $num\n";
+    ++$num;
+} while ($num < 5);
+
+// "for" loops allow you to create a more concise while loop.
+// Inside the parentheses, the left section creates a variable before the loop
+// starts, the middle section is the check that is done at the beginning of each loop
+// and the third section is executed after each loop.
+for ($i = 0; $i < 10; $i++) {
+    echo "For loop $i\n";
+}
+
+// A "foreach" loop allows you to easily loop over an array.
+// An array is a list of data stored together.
+// The "as" keyword lets you assign a variable to the value
+// in the array for the current iteration of the loop.
+$set = [1, 2, 3, 4, 5];
+foreach ($set as $num) {
+    echo "Array value $num\n";
+}
+
+// In loops, you can use the keyword "break" to stop the loop execution
+// no matter how many more iterations should run.
+$values = ['one', 'two', 'three'];
+foreach ($values as $value) {
+    if ($value === 'two') {
+        break;
+    }
+    echo "Break $value\n";
+}
+
+// The "continue" keyword stops executing the current loop iteration,
+// but then allows the loop to continue with other iterations.
+$values = ['one', 'skip', 'three'];
+foreach ($values as $value) {
+    if ($value === 'skip') {
+        continue;
+    }
+    echo "Continue $value\n";
+}

code/variables.php

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+<?php
+
+// The variable is the basic building block of any programming language.
+// In PHP, all variables start with a dollar sign.
+$greeting;
+
+// To set data in a variable, you put an equals sign after it and some data.
+$greeting = 'Hello World!';
+
+// Once you create a variable, you can use it again in other commands and functions.
+echo $greeting;
+
+// After the dollar sign, a PHP variable must have an alphabetic character or underscore. Also, variables are case sensitive.
+$_var = 'I am a variable with an underscore!';
+$Var = 'I am a variable with a capital letter!';
+$var = 'I am a new variable';
+
+// Variables can hold many different types of data, but there are four simple ones you can try now.
+// An int is a number without a decimal place.
+// A float is a number with a decimal place.
+// A boolean can be two values: true or false.
+// Last, there is a string, a collection of characters.
+$int = 1;
+$float = 100.10;
+$bool = true;
+$string = 'I am a string';
+
+// In other programming languages, you have to write what type of data the variable will contain.
+// PHP keeps it simple by allowing you to put any type of data in a variable, including already used variables.
+$number = 1;
+$number = 'one';