Initial commit for public repo

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";