Chapter 2 - Gaining Control with Operators and Flow Control spring into PHP 5 by Steven Holzner

1. Chapter 2 - Gaining Control with Operators and Flow Controlspring into PHP 5by Steven Holzner Slides were developed by Jack DavisCollege of Information Scienceand TechnologyRadford University

2. PHP Operators and Flow Control • Math Operators+ Adds numbers- Subtracts numbers* Multiplies numbers/ Divides numbers% returns integer remainder from integer division<?php echo "5+2 = ", 5+2, "<br />";?> • Math Functionsabs Absolute ValueYou call functions the same as you do in most languages. Use the name of the function and provide the appropriate arguments.$y = abs(-9);echo "$y";

3. List of Math Functions • Here's some of the commonly used functions. More are listed in the text, p. 35.ceil rounds fractions upexp calculates the exponent of efloor rounds fractions downfmod returns the floating point remainder of the division of the argumentsis_nan determines whether a value is not a numbermax finds the highest valuemin finds the lowest valuesqrt square root

4. Assignment Operator • As in most languages the assignment operator is =.This means the expression on the right of the operator is evaluated and the resulting value is stored in the variable on the left.$a = 4 + 3 + $b. • There are also combined assignment operators.+= -+ *= /=.= %= |= ^=<<= >>=$a += $b;We'll see more of these in use later.

5. Incrementing & Decrementing • PHP includes the ++ and the -- operators that can be used pre and post for some operation.++$value increments $value by one, then returns $value--$value decrements $value by one, then returns $value$value++ returns $value, then increments$value-- returns $value, then decrements<?php $a = $b = $c = $d = 1; echo "\$a++ gives ", $a++, "<br />"; echo "++\$b gives ", ++$b, "<br />";?>ouputs what ?

6. Operator Precedence • new • [ • ! ~ ++ -- (int) (float)(string) (array) (object) • @ • * / % • + - . • << >> • < <= > >= • == != === !== • & • ^ • | • && • || • ? : • = += -+ and so onthere are more. use parentheses to avoid problems.

7. Execution Operator • The execution operator lets you run operating system commands and programs, enclose the command in backquotes (`).<?php $output = `date`; echo $output;?>In a Unix system using bash -- Fri Aug 25 12:30:42 EDT 2006 • you can pass an argument to the system command<?php $output = `ls -l *.php`; echo $output;?> • https://php.radford.edu/~jcdavis/it325examples/execop.php

8. String Operators • PHP has two string operators. concatenation .concatenating assignment .= • <?php $a = "ITEC"; $b = 325; $c = $a . " " . $b; #note coercion # now $c = "ITEC 325" $a .= " " . $b; // now $a = "ITEC 325"?> • we'll see many more string function in PHP in the next chapter

9. Bitwise Operators • PHP has a set of operators that can work with the individual bits in an integer. Note - Besides integers, you can also work with strings using these operators; in that case, the ASCII value of each character is used.

10. if Statements • Just the standardif (boolean expression) php statement;if the boolean expression evaluates to true the statement beneath is executed, otherwise it is not executedcan execute more than one statement by createing a block of statements using { }if (boolean expression) { phpstatement 1; php statement 2; php statement 3; }$a = 50;if ($a > 45) echo "\$a's value is: $a";

11. Comparison Operators

12. Logical Operators

13. else and elseif • $a = 20; $b = 40;$c = "40chairs";if ($a >= $b) { echo "\$a is larger, value is : $a"; }else { echo "\$b is larger, value is : $b";}if ($a == $c) { echo "a & c are the same."; }else { echo "a & c are not the same."; }if ($a === $c) { echo "a & c are the same."; }elseif ($a == $c) { echo "a & c are different types."; }else {echo "a & c have different values."} • comparisons of strings and characters are based on the ASCII character codes

14. switch Statements • switch statements are used for testing multiple conditions. The same tests can be built with multiple if statements, however, switch statements help to organize code.(use ints, floats, or strings)$temp = 70;switch ($temp) { case 70: echo "Nice weather."; break; case 80: { echo "Warm today. <br />"; echo "Old bones like warm weather."; break; } case 90: echo "Hot!!!"; break; default: echo "temperature not in range"; }

15. for Loops • for (expression1;expression2;expression3) statement;for ($ctr = 1; $ctr < 10; $ctr++) { print ("\$ctr = : $ctr <br />"); } • expressions in a for loop can handle multiple indexes, as long as you separate them with the comma operator.for ($var1=2, $var2=2; $var1<5; $var1++) { echo "var1 is : $var1 ", " double it : $var1 * $var2 ": } • probably easier to use nested for loops

16. while Loops • standard loop that keeps executing until the initial condition is false$ind = 10;while ($ind > 1) { echo "ind = $ind"; $ind--; } • often used when reading filesopen_file();while (not_at_end_of_file()) { $data = read_one_line_from_file(); echo $data; }

17. do … while Loops • just like a while loop except the condition is checked at the end of the loop instead of the beginning, so it's always executed at least oncedo { echo $val, "<br />"; $val *= 2; } while ($val < 10);

18. foreach Loops & break • the foreach loop makes working with arrays much easier.<?php $arr = array("apples","oranges","grapes"); foreach ($arr as $value) { echo "Current fruit: $value <br />"; } • in case you want to stop a loop or swich statement early, the break statement ends execution of the current for, foreach, while, do…while, or switch statement.while (not_at_end_of_file()) { $data = read_one_line_from_file(); echo $data; if ($data == "quit") break; }

19. continue Statement • the continue statement can be used inside a loop to skip the rest of the current loop iteration and continue with the next iteration.for ($val = -2; $val < 2; $val++) { if ($val == 0) { continue; } echo 1/$val, " <br />"; }skipped the division by 0 • php has alternate syntax for if, while, for, foreach, and switch statementsfor ($ctr=0; $ctr < 5; $ctr++): echo "Print this five times.";endfor;