Lecture 2 php basics (1)

PHP BasicsPrepared By: Mary Grace G. Ventura 

PHP Scripting BlockAlways starts with <?php and ends with ?><html><head><title>Hello World Script</title></head><body><?php echo “Hello World!”?></body></html>

Using Simple StatementsSimple statements are an instruction to PHP to do one simple action.There are two basic statements to output text with PHP: echo and print. Note: The file must have a .php extension. If the file has a .html extension, the PHP code will not be executed.

echo commandThe simplest use of echo is to print a string as argument, for example:echo “This will print in the user’s browser window.”;Or equivalentlyecho(“This will print in the user’s browser window.”);

Echo StatementYou can also give multiple arguments to the unparenthesized version of echo, separated by commas, as in:echo “This will print in the “, “user’s browser window.”;The parenthesized version, however, will not accept multiple arguments:echo (“This will produce a “, “PARSE ERROR!”);

Used of \n- newline echo “line 1\n”; echo “line 2”;Will producedline 1 line 2Used of echo “line 1 ”; echo “line 2”;Will producedline 1line 2Used of and \n

PHP Simple StatementsFollow These Rules:PHP statements end with a semicolon or the PHP ending tag. PHP doesn’t notice white space or the end of lines. It continues reading a statement until it encounters a semicolon or the PHP closing tag, no matter how many lines the statement spans.PHP statements may be written in either upper- or lowercase. In an echo statement, Echo, echo, ECHO, and eCHo are all the same to PHP.

Comments in PHPIn PHP, we use // to make a single-line comment or /* and */ to make a large comment block. <?php //This is a line comment # or this one /* This is a comment block */?>

VariablesAre used for storing values such as numbers and strings so that it can be used several times in the script. “Symbolic Representation of a value”.Variables are identified and defined by prefixing their name with a dollar sign Example: $variable1, $variable2Variable names must start with a letter or underscore character (“_”)Variable names may contain letters, numbers, underscores, or dashes. There should be no spaces Variable names are CaSE- SeNSiTiVE$thisVar$ThisvAr

Example of Variable Names$item$Item$myVariable (camel case)$this_variable$this-variable$product3$_book$__bookPage

VariablesPHP variables are not declared explicitly instead they are declared automatically the first time they are used.It’s a loosely typed of language so we do not specify the data type of the variable.PHP automatically converts the variable to the correct data type such as string, integer or floating point numbers.

Illustration of a Variable Declaration

Example of Variable Variables$varName=“ace”;$$varName=1029;This is exactly equivalent to$ace=1029;

ConstantsAlways stay the same once definedConstants are defined with the define() function. Example: define(“VARIABLE1”, “value”);Constant names follow the same rules as variable namesConstants are typically named all in UPPERCASE but do not have to be.

ConstantsOne important difference between constants and variables is that when you refer to a constant, it does not have a dollar sign in front of it.If you want to use the value of a constant, use its name only.define(‘OILPRICE’,10);echo OILPRICE;

Sample Program for Constant Declaration<?php define(“USER”,”Grace”); echo “Welcome ” . USER;?>Output:Welcome Grace

IntegerAn integer is a plain-vanilla number like 75, -95, 2000,or 1.Integers can be assigned to variables, or they can be used in expressions, like so:$int_var = 12345;

Floating PointA floating-point number is typically a fractional number such as 12.5 or 3.149391239129.Floating point numbers may be specified using either decimal or scientific notation.Ex: $temperature = 56.89;

DoublesDoubles are floating-point numbers, such as:$first_double = 123.456;$second_double = 0.456$even_double = 2.0;Note that the fact that $even_double is a “round” number does not make it an integer. And the result of:$five = $even_double + 3;is a double, not an integer, even if it prints as 5. In almost all situations, however, you should feel free to mix doubles and integers in mathematical expressions, and let PHP sort out the typing.

BooleanThe simplest variable type in PHP, a Boolean variable simply specifies a true or false value.TRUE=1, FALSE=0Case-InsensitiveTrue, TRUE, true are all the same.Printing out Boolean values.echo true . “\n”; //prints trueecho false; //(none)1(none)

BooleanThe ff. are considered FALSE:Integers and floats zero(0)Empty String (“”)The string “0”Array with zero elementsNULLObject with zero member variablesEvery other value is considered TRUE.

NULLNull is a special value that indicates no value.Case-insensitiveNULL, null, NullNULL converts to boolean FALSE and integer zero.A variable is considered to be NULL if:It has been assigned to the constant NULLIt has not been set to any value yetIt has been unset<?php$a= NULL;echo $b; ?>

isset(), is_null()isset()Tests if a variable existsReturns FALSE if:Is set to NULLVariable has been unset()is_null()Determines if the given variable is set to NULL.Returns true if variable is NULL, FALSE otherwise.

empty()Determines if a variable is empty.The following values are considered empty:

isset() vs empty() vs is_null()

StringsA string is a sequence of characters, like 'hello' or 'abracadabra'. String values may be enclosed in either double quotes ("") or single quotes ('').$name1 = ‘Ervin';$name2 = ‘Grace’;

Singly Quoted StringsExcept for a couple of specially interpreted character sequences, singly quoted strings read in and store their characters literally.$literally = ‘My $variable will not print!\\n’;print($literally);produces the browser output:My $variable will not print!\\n

Doubly Quoted StringsStrings that are delimited by double quotes (as in “this”) are preprocessed in both the following two ways by PHP:Certain character sequences beginning with backslash (\) are replaced with special characters.Variable names (starting with $) are replaced with string representations of their values.

Escape Sequence Replacements Are:\n is replaced by the new line character \r is replaced by the carriage-return character\t is replaced by the tab character\$ is replaced by the dollar sign itself ($)\” is replaced by a single double-quote (“)\\ is replaced by a single backslash (\

A Note on String Values<?php$identity = 'James Bond'; $car = 'BMW'; // this would contain the string // "James Bond drives a BMW"$sentence = "$identity drives a $car"; // this would contain the string // "$identity drives a $car"$sentence = '$identity drives a $car';?>

A Note on String Values<?php// will cause an error due to// mismatched quotes$statement = 'It's hot outside';// will be fine$statement = 'It\'s hot outside';?>

Data ConversionIn PHP, the type of the variable depends on the value assigned to it.

TypecastingThere are circumstances in which you will want to control how and when individual variables are converted from one type to another.This is called typecastingTypecasting forces a variable to be evaluated as another typeThe name of the desired type is written in parentheses before the variable that is to be cast.

Typecasting-IntegersYou can typecast any variable to an integer using the (int) operator.Floats are truncated so that only their integer portion is maintained.echo (int) 99.99; //99Booleans are cast to either one or zero(int) TRUE == 1(int) FALSE == 0Strings are converted to their integer equivalentecho (int) “test 123” ; //0echo (int) “123”;echo (int) “123test”;NULL always evaluates to zero.

Typecasting BooleansData is cast to Boolean using the (bool) operatorecho (bool) “1”;Numeric values are always TRUE unless they evaluate to zeroStrings are always TRUE unless they are empty(bool) “FALSE” ==trueNull always evaluates to FALSE.

Typecasting- StringsData is typecast to a string using the (string) operator:echo (string) 123;Numeric values are converted to their decimal string equivalent:(string) 123.1 == “123.1”;Booleans evaluate to either “1” (TRUE) or an empty string (FALSE)NULL values evaluates to an empty string.

Gettype()Gets the type of a variableReturns “boolean”, “integer”, “double”, “string”, “array”, “object”, “resource”, “NULL”.

settype()Sets the type of a variable“boolean”, “integer”, “double”, “string”, “array”, “object”, “resource”, “NULL”

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