4. PHP Code Flow Control - PHP & MySQL Web Development


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Basic concepts about PHP code flow control
Telerik Software Academy: http://academy.telerik.com/school-academy/meetings/details/2011/10/11/php-school-academy-meeting
The website and all video materials are in Bulgarian.

This lecture discusses the following topics:

Conditional statements
Functions and return values
Include and require
Variables scope

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4. PHP Code Flow Control - PHP & MySQL Web Development

  1. 1. Code Flow Control Loops, Conditional Statements, FunctionsRadoslav Georgievhttp://rado-dev.comGameCraftwww.game-craft.com
  2. 2. Recap We talked about  How to install a Web Server that runs PHP  How to create PHP files and run them on the browser and inside the console  How to define variables in PHP – with $  How to define Constants – with define(‘name’,value)  How to deal with Strings  Some predefined constants and superglobals 2
  3. 3. Contents1. Loops2. Conditional statements3. Functions and return values4. Include and require5. Variables scope
  4. 4. Loops
  5. 5. The while Structure expression PHP supports the C style while loop $a = 1; while ($a < 100) { $a ++; echo $a; } body  The body of the cycle will be executed until the condition is met  The body consists of one or more statements  If more than one, surrounding brackets are required  The condition expression is of type boolean
  6. 6. The While Structure Live Demo
  7. 7. do… while Structure The do-while structure is similar to while-do  The condition is checked after the body is executed!  The body is executed at least once! body $a = 1; do { $a ++; expression echo $a; } while ($a < 100); // this will produce 2 3 4 … 100 // the while cycle would output 2 3 4 … 99
  8. 8. do… while Structure Live Demo
  9. 9. for Cycle PHP supports C style for cycles for ($i = 0; $i < 10; $i++) echo $i;  The for cycle requires initialization, iteration and ending condition statement body  None of them are obligatory  Each statement can consist of multiple comma separated statements initializationconditioniteration end for ($i = 0, $j = 10; ; $i++, $j--) if ($j > $i) echo $i; else break;
  10. 10. for Cycle Live Demo
  11. 11. foreach Foreach is used to iterate over arrays $arr = array (1,1,2,3,5,8); foreach ($arr as $value) echo $value;  For each element in the array the body of the cycle will be called  $value will be assigned the value of the current element in the array
  12. 12. foreach and Associative Arrays Foreach has second form $arr = array ("one" => 1, "two" => 2); foreach ($arr as $key => $value) echo $key." => ".$value;  Allows you to access the key, corresponding to the value in the array
  13. 13. foreach Live Demo
  14. 14. break and continue You can leave a cycle with the break command You can move immediately to next cycle iteration with continue command $i = 0; while (true) { $i ++; if ($i == 10) break; // exit the cycle if ($i%2 == 0) continue; // next iteration echo $i; } // will print out 1 3 5 7 9
  15. 15. break andcontinue Live Demo
  16. 16. Conditional Statements
  17. 17. Conditional Statements - if if construct allows code to be executed only if Boolean expression certain condition is met the brackets! Dont forget $a = 5; $b = 7; if ($a > $b) echo "A is greater than B"; if ($a % 2) { echo "A is odd"; $b = $a % 2; Code block to execute if echo "A%2 is expression is true :".$b; }  Note: assignment returns as value the one being assigned. So we can have if ($b = $a%2) echo "A is odd - A%2 is :".$b;
  18. 18. If - else if-else construct is extension of if construct and allows you to execute one code if condition is met or another if not $a = 5; $b = 7; if ($a > $b) echo "A is greater than B"; else echo "B is greater or equal to A";
  19. 19. If - else Live Demo
  20. 20. if - elseif Extension of the if-else construct  Allows you to add conditions for the else body if ($a > $b) echo "A is greater than B"; elseif ($a == $b) echo "A is equal to B"; else echo "B is greater than A";  It is similar to writing else if and have two conditional statements  You can have multiple elseif statements
  21. 21. if - elseif Live Demo
  22. 22. switch switch structure allows you to execute different code, depending on the value of variable  It is similar to writing a lot if-s  The switch body contains "case" clauses  The engine finds the clause that matches the value and jumps to that part of the code switch ($a) { case 0: echo "A is 0"; break; case 1: echo "A is 1"; break; }
  23. 23. switch (2) Similarto else, you can have default case in a switch  If no case option is found the engine jumps to the default option switch ($a) { case 0: echo "A is 0"; break; case 1: echo "A is 1"; break; default: echo "A is … something else"; break; }  The default case is not obligatory the last one
  24. 24. switch(3) When the engine moves to the found case it does NOT exit after the code of that case but moves on to the next one $a = 0; switch ($a) { case 0: echo "A is 0"; case 1: echo "A is 1"; }  This example will output "A is 0 A is 1"  The solution is to add break where necessary  This applies to the default case too
  25. 25. switch(4) Due to the behavior of the switch engine, you can use empty cases  They are without break so the engine will jump to them and move on  You can use this to combine multiple values with single code $a = 0; switch ($a) { case 0: echo "A is 0"; break; case 1: case 2: echo "A is 1 or 2"; break; }
  26. 26. switch(5) You can use any scalar type of variable (string, number, boolean, etc) switch ($name) { case "Dimitar": echo 1; break; case "Svetlin": case "Nakov" : echo 2; break; case false : echo "No name"; break; default : echo "?!"; break; }
  27. 27. switch (6) Keep in mind switchuses the loose comparison "==" and may lead to unexpected results! The solution: $v = ""; switch (true) { case ($v === false): echo "its boolean false"; break; case ($v === 0): echo "its numeric zero"; break; case ($v === null): echo "its null variable"; break; case ($v === ""): echo "its empty string"; break; }
  28. 28. switchLive Demo
  29. 29. Ternary Operator The ternary operator is short version of if- else construct  It is used only to return one value or another, depending on condition  The syntax is: <condition>?<value if true>:<value if false> echo ($a<$b ? "a is smaller" : "b is smaller"); echo ($a>$b ? "a" : "b")." is greater"; $b = ($a % 2 ? 17 : 18);  You cannot use it like this: ($a > 17 ? echo "a" : echo "b" );
  30. 30. Ternary Operator Live Demo
  31. 31. Functions
  32. 32. Functions Functions are sets of statements, combined under unique name  Declare with statement function  Can accept parameters and return value  Helps organize and reuse the code  Echo, print and others are inbuilt functions function sum ($a, $b) { return $a + $b; } echo sum(5,7); // will output 12
  33. 33. Functions (2) The name of the function must be unique Can accept unlimited number of arguments  The are defined in brackets after the function name Can return value with return statement  Accepts one parameter – the return value
  34. 34. Functions parameters Function can have predefined value for its parameters  Simplifies its usage function max ($a, $b, $strict = true) { if (strict) return ($a > $b); else return ($a >= $b); } echo max(3,3,false); echo max(4,3,true); echo max(3,3); // we can omit 3rd parameter  The default value must be constant expression  The defaulted arguments must be on the right side in the function declaration!
  35. 35. Functions Live Demo
  36. 36. Functions Parameters (2) By default PHP passes arguments to functions by value  This means change of argument value in the function will not have effect after function ends  You can force it to pass argument by reference with & prefix of the argument function double (&$a) { $a *= 2; } $b = 7; double ($b); echo $b; // will return 14;
  37. 37. Function Parameters (3) PHP supports variable-length function parameters  You can pass any number of arguments to the function  The function can read the parameters with func_num_args() and func_get_arg() function sum(){ $res = 0; for ($i=0, $n = func_num_args(); $i < $n; $i++) $res += func_get_arg ($i); return $res; } echo sum (4,5,6);
  38. 38. Function Return Values Functions can return values with the return statement  Accepts only one argument – the value to be returned  Exits the function function foo ($a) { return true; // the following code will NOT be executed echo $a + 1;  } return multiple values you can use arrays To  Function is not obligatory to return value
  39. 39. Function Return Values (2) You can use fixed-size arrays to return multiple values and the list statement function small_numbers () { return array (0,1,2); } list ($a, $b, $c) = small_numbers();  The list statement assigns multiple array items to variables  This is NOT a function like array  Works only for numerical arrays and assumes indexes start at 0
  40. 40. Variable Functions PHP supports variable functions  If variable name has parentheses appended to it the engine tries to find function with name whatever the function value is and executes it function foo () { echo "This is foo"; } $a = foo; $a(); // this calls the foo function  This doesnt work with some inbuilt functions like echo, print, etc
  41. 41. Variable Functions Live Demo
  42. 42. Few Notes on Functions You can check if function is declared with function_exists($name)  Useful to create cross-platform scripts Functions can be declared inside other functions  They do not exist until the outer function is called Functions can be defined conditionally  Depending on condition function can be defined or not
  43. 43. Include and Require
  44. 44. Include and Require include and require are statements to include and evaluate a file  Useful to split, combine and reuse the code  Both accept single parameter – file name require "header.php"; echo "body comes here"; require "footer.php";  If file is not found include produces warning, require produces fatal error  File can be with any extension
  45. 45. include_once and require_once include_once and require_once are forms of include and require  With include and require you can include one file many times and each time it is evaluated  With include_once and require_once if file is already included, nothing happens  For instance if in the file you have declared function, double including will produce error "Function with same name already exists"
  46. 46. IncludeLive Demo
  47. 47. Variables Scope
  48. 48. Variables scope Variables, declared in functions exist only until the function is over Files being included/required inherit the variable scope of the caller The arrays $_GET, $_POST, $_SERVER and other built-in variables are global  Can be accessed at any place in the code Variablesdeclared outside function are not accessible in it
  49. 49. The Global Keyword Variables outside function are not accessible in it $a = "test"; function $foo () { echo $a; // this will not output anything }  They have to be global or function must declare it will use them with global $a = "test"; function $foo () { global $a; echo $a; // this will output "test"; }
  50. 50. Loops and Variable Scope Variables, declared in loops are not accessible after loop is over for ($i = 0; $i < 5; $i++) { $arr[] = $i; } print_r ($arr); // outputs nothing  In the example you have to declare the array before the loop $arr = array(); for ($i = 0; $i < 5; $i++) { $arr[] = $i; } print_r ($arr); // this time works
  51. 51. Note on Brackets As PHP code can be embedded in HTML, HTML code can be embedded in PHP code <?php if ($name == "John") { ?> Hello John! <?php } ?>  This is similar to writing echo "Hello John!";  Very useful for long texts
  52. 52. Code Flow Control курсове и уроци по програмиране, уеб дизайн – безплатно BG Coder - онлайн състезателна система - online judge курсове и уроци по програмиране – Телерик академия форум програмиране, форум уеб дизайн уроци по програмиране и уеб дизайн за ученици ASP.NET курс - уеб програмиране, бази данни, C#, .NET, ASP.NET http://academy.telerik.com програмиране за деца – безплатни курсове и уроци ASP.NET MVC курс – HTML, SQL, C#, .NET, ASP.NET MVC безплатен SEO курс - оптимизация за търсачки алго академия – състезателно програмиране, състезаниякурсове и уроци по програмиране, книги – безплатно от Наков курс мобилни приложения с iPhone, Android, WP7, PhoneGap уроци по уеб дизайн, HTML, CSS, JavaScript, Photoshop Дончо Минков - сайт за програмиране free C# book, безплатна книга C#, книга Java, книга C# Николай Костов - блог за програмиране безплатен курс "Качествен програмен код" безплатен курс "Разработка на софтуер в cloud среда" C# курс, програмиране, безплатно
  53. 53. Exercises1. Write a program that prints the numbers from 1 to 502. Write a program that prints the numbers from 1 to 50 that are not divisible by 5 and 73. Write a program that prints HTML table with N columns and N rows with the numbers 1, 2, 3, ... in its cells for a given N, defined as a constant4. Write a program that finds the minimal element of an given indexed array
  54. 54. Exercises (2)5. Write a program that calculates N! (factorial 1*2*..*N) for a defined constant N6. Write a program that calculates N!*K!/(N-K)! for defined constants N and K7. Write a program that prints the binary representation of a decimal number N, defined by a constant8. Write a program that prints the decimal representation of a binary number, defined in a string
  55. 55. Free Trainings @ Telerik Academy “PHP & MySQL Web Design" course academy.telerik.com/.../php-school- academy-meeting Telerik Software Academy  academy.telerik.com Telerik Academy @ Facebook  facebook.com/TelerikAcademy Telerik Software Academy Forums  forums.academy.telerik.com