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Chapter 1 Language Basic

Chapter 1 Language Basic

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Chapter 1 Language Basic

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  1. Chapter 1 Language Basic

  2. Chapter Goals • This chapter provides a whirlwind tour of the core PHP language, covering such basic topics as: • Basic Rules • data types • Variables • Operators • flow control statements • We start with the basic units of a PHP program and build up your knowledge from there.

  3. Basic Rules • Case Sensitivity • The names of user-defined classes and functions, as well as built-in constructs and keywords such as echo, while, class, etc., are case-insensitive. Thus, these three lines are equivalent: echo("hello, world"); ECHO("hello, world"); EcHo("hello, world"); • Variables, on the other hand, are case-sensitive. That is, $name, $NAME, and $NaME are three different variables.

  4. statement is a collection of PHP code that does something. Here is a small sample of PHP statements : echo "Hello, world"; myfunc(42, “John"); $name = “smith"; if ($a == $b) { echo “Correct?"; } PHP uses semicolons to separate simple statements. Semicolon before the closing brace is optional <?php if ($a == $b) { echo "Rhyme? And Reason?"; } echo “Web Programming with PHP“ ?> Statements and Semicolons

  5. Whitespace and Line Break • In general, whitespace doesn't matter in a PHP program. • For example, this statement: myfunc(42, “John"); myfunc( 42 , “John“ );

  6. Comment • Comments give information to people who read your code, but they are ignored by PHP • For single line: // comment text or # comment text • $x = 17; // store 17 into the variable $x whereas this • For multiple line: /* comment text */ • <?php /* if ($a == $b) { echo "Rhyme? And Reason?"; } */ echo “Web Programming with PHP“ • ?>

  7. Variables • variable is a special container that you can define to "hold" a value. • PHP is a weakly typed language, the data type of a variable can change as we change the data that it contains . • Rules for Naming Variables: • Variable names should begin with a dollar($) symbol. • Variable names can begin with an underscore. • Variable names cannot begin with a numeric character. • Variable names must be relevant and self-explanatory. • Here are some examples of valid and invalid variable names: • $salary valid • $_firstname valid • sex invalid: doesn’t start with dollar sign($) • $12result invalid: starts with number; it doesn’t start with letter or underscore

  8. Variable Variables • You can reference the value of a variable whose name is stored in another variable. For example: <?php $first = “hello”; $$first = “World”; echo “the value of the first variable is $first”; echo ”the value of the second variable is $hello ”; ?> • After these two statement executes, the variable $first has the value "hello", and the variable $hello has the value “World”.

  9. Variable References • In PHP, references are how you create variable aliases. To make $black an alias for the variable $white, use: $black =& $white; $big_long_variable_name = "PHP"; $short =& $big_long_variable_name; $big_long_variable_name .= " rocks!"; print "\$short is $short\n"; print "Long is $big_long_variable_name\n";

  10. Variable Scope • The scope of a variable determines those parts of the program that can access it. • There are four types of variable scope in PHP: local, global, static, and function parameters.

  11. 1). Local scope • A variable declared in a function is local to that function. That is, it is visible only to code in that function function update_counter ( ) { $counter++; Echo $counter; } $counter = 10; update_counter( ); echo $counter; //It will print 10

  12. 2.) Global scope • Variables declared outside a function are global. That is, they can be accessed from any part of the program • To allow a function to access a global variable, you can use the global keyword inside the function to declare the variable within the function. function update_counter ( ) { global $counter; $counter++;} $counter = 10; update_counter( ); echo $counter; #It will print 11

  13. 3.)Static variables • A static variable retains its value between calls to a function but is visible only within that function. • You declare a variable static with the static keyword. function update_counter ( ) { static $counter = 0; $counter++; echo "Static counter is now $counter\n"; } $counter = 10; update_counter( ); update_counter( ); echo "Global counter is $counter\n";

  14. Data Types • PHP provides four primitive data types: integers, floating point numbers, strings, and booleans 1.) Integers • Integers are whole numbers • integer values range from -2,147,483,648 to +2,147,483,647 • PHP automatically converts larger values to floating point numbers if you happen to overflow the range. • Use the is_int( ) function (or its is_integer( ) alias) to test whether a value is an integer. • PHP will accept integer values using three mathematical bases: decimal (base 10), octal (base 8), and hexadecimal (base 16). • Example: $decimal=16; $hex=0x10; $octal=020;

  15. 2.) Floating Point Numbers • Floating point numbers represent decimal values. • a double can be between 1.7E-308 to 1.7E+308. • A double may be expressed either as a regular number with a decimal point or in scientific notation • example: $var=0.017; $var=17.0E-3. • Use the is_float( ) function (or its is_real( ) alias) to test whether a value is a floating point number 3.) Strings • A string is a sequence of characters. A string can be delimited by single quotes or double quotes. • Double-quoted strings are subject to variable substitution and escape sequence handling, while single quotes are not. • Use the is_string( ) function to test whether a value is a string

  16. <?php $my_int = 50; $string_one = "The value of the variable is $my_int<BR>"; $string_two = 'The value of the variable is $my_int<BR>'; echo $string_one; echo $string_two; ?> Escape Sequence

  17. Type Casting • Type casting uses the C-style syntax in which you put the type you want in brackets before the variable or expression. • example: $var = (int)"123abc";

  18. Operators and Expressions 1.) Assignment Operator • It consists of the single character =. • The assignment operator takes the value of its right-hand operand and assigns it to its left-hand operand: $name = “Norton"; 2.) Arithmetic Operators

  19. Operators and Expressions 3.)Concatenation Operator • The concatenation operator is represented by a single period(“.”): $name=“PHP”; echo “Norton"." University“; echo “your name is ”.$name; 4.) Combined Assignment Operators • A combined assignment operator consists of a standard operator symbol followed by an equals sign

  20. Operators and Expressions 5.)Comparison Operators • They return the Boolean value true if the test is successful, or false otherwise.

  21. Operators and Expressions 6.) Logical Operators • The logical operators test combinations of Booleans

  22. Constants • You must use PHP's built-in define() function to create a constant • To use the define() function, you must place the name of the constant and the value you want to give it within the call's parentheses. • These values must be separated by a comma <?php define( "CONSTANT_NAME", 42); Echo”The value is ”.CONSTANT_NAME; ?> • The define() function can accept a third Boolean argument that determines whether or not the constant name should be case-independent • By default, constants are case-dependent

  23. Conditional Statements 1.) The if Statement • The if statement evaluates an expression between parentheses if ( expression ) { // code to execute if the expression evaluates to true } <?php $mood = "happy"; if ( $mood == "happy" ) { print "Hooray, I'm in a good mood"; } ?>

  24. Conditional Statements 2.) Using the else Clause with the if Statement if ( expression ) { // code to execute if the expression evaluates to true } else { // code to execute in all other cases } <?php $mood = "sad"; if ( $mood == "happy" ) { print "Hooray, I'm in a good mood"; } else { print "Not happy but $mood"; } ?>

  25. Conditional Statements 3.) Using the elseif Clause with the if Statement • You can use an if...elseif...else construct to test multiple expressions before offering a default block of code if ( expression ) { // code to execute if the expression evaluates to true } elseif (another expression) { // code to execute if the previous expression failed // and this one evaluates to true } else { // code to execute in all other cases } NOTE:The elseif clause can also be written as two separate words (else if).

  26. Conditional Statements <?php $mood = "sad"; if ( $mood == "happy" ) { print "Hooray, I'm in a good mood"; } elseif ( $mood == "sad" ) { print "Awww. Don't be down!"; } else { print "Neither happy nor sad but $mood"; } ?>

  27. Conditional Statements 4.) The switch Statement switch ( expression ) { case result1: // execute this if expression results in result1 break; case result2: // execute this if expression results in result2 break; default: // execute this if no break statement // has been encountered hitherto }

  28. Conditional Statements <?php $mood = "sad"; switch ( $mood ) { case "happy": print "Hooray, I'm in a good mood"; break; case "sad": print "Awww. Don't be down!"; break; default: print "Neither happy nor sad but $mood"; } ?>

  29. Conditional Statements 5.) Using the ? Operator • The ? or ternary operator is similar to the if statement but returns a value derived from one of two expressions separated by a colon. ( expression )?returned_if_expression_is_true:returned_if_expression_is_false; <?php $mood = "sad"; $text = ($mood=="happy") ? "I'm in a good mood" : "Not happy but $mood"; print "$text"; ?>

  30. Looping Statements 1.) The while Statement while ( expression ) { // do something } <?php $counter = 1; while ( $counter <= 12 ) { print "$counter times 2 is ".($counter*2)."<br>"; $counter++; } ?>

  31. Looping Statements 2.) The do...while Statement • The essential difference between the two is that the code block is executed before the truth test and not after it do { // code to be executed } while ( expression ); <?php $num = 1; do { print "Execution number: $num<br>\n"; $num++; } while ( $num > 200 && $num < 400 ); ?>

  32. Looping Statements 3.) The for Statement for ( initialization expression; test expression; modification expression ) { // code to be executed } <?php for ( $counter=1; $counter<=12; $counter++ ) { print "$counter times 2 is ".($counter*2)."<br>"; } ?>

  33. Looping Statements 4.) Breaking Out of Loops with the break Statement • The break statement enables you to break out of a loop based on the results of additional tests <?php for ( $counter=-4; $counter <= 10; $counter++ ) { if ( $counter == 0 ) break; $temp = 4000/$counter; print "4000 divided by $counter is... $temp<br>"; } ?>

  34. Looping Statements 5.)Skipping an Iteration with the continue Statement • The continue statement ends execution of the current iteration but doesn't cause the loop as a whole to end. • Instead, the next iteration begins immediately. <?php for ( $counter=-4; $counter <= 10; $counter++ ) { if ( $counter == 0 ) continue; $temp = 4000/$counter; print "4000 divided by $counter is... $temp<br>"; } ?>

  35. Looping Statements 6.) Nesting Loops • Loop statements can contain other loop statements. <?php print "<table border=\"1\">\n"; for ( $y=1; $y<=6; $y++ ) { print "<tr>\n"; for ( $x=1; $x<=6; $x++ ) { print "\t<td>"; print ($x*$y); print "</td>\n"; } print "</tr>\n"; } print "</table>"; ?>

  36. The end of Chapter 1 Thanks for your paying attention