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T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 112 Note PHP statements are terminated by semicolon (;). The closing tag of a block of PHP code also automatically implies a semicolon (so you do not have to have a semicolon terminating the last line of a PHP block). T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 113 Comments in PHP A comment in PHP code is a line that is not read/executed as part of the program. Its only purpose is to be read by someone who is editing the code! Comments are useful for: To let others understand what you are doing Comments let other programmers understand what you were doing in each step (if you work in a group) To remind yourself what you did - Most programmers have experienced coming back to their own work a year or two later and having to re-figure out what they did. Comments can remind you of what you were thinking when you wrote the code T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 114 Example PHP supports three ways of commenting: T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 115 PHP Case Sensitivity In PHP, all user-defined functions, classes, and keywords (e.g. if, else, while, echo, etc.) are NOT case-sensitive. In the example below, all three echo statements below are legal (and equal): T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 116 Example "; echo "Hello World!"; EcHo "Hello World!
"; ?> T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 117 PHP Case Sensitivity However; in PHP, all variables are case-sensitive. In the example below, only the first statement will display the value of the $color variable (this is because $color, $COLOR, and $coLOR are treated as three different variables): T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 118 Example "; echo "My house is " . $COLOR . "
"; echo "My boat is " . $coLOR . "
"; ?> T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 119 PHP Variables Variables are "containers" for storing information: Example T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 120 Much Like Algebra x=5 y=6 z=x+y In algebra we use letters (like x) to hold values (like 5). From the expression z=x+y above, we can calculate the value of z to be 11. In PHP these letters are called variables. T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 121 PHP Variables As with algebra, PHP variables can be used to hold values (x=5) or expressions (z=x+y). A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume). Rules for PHP variables: A variable starts with the $ sign, followed by the name of the variable A variable name must start with a letter or the underscore character A variable name cannot start with a number A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ ) Variable names are case sensitive ($y and $Y are two different variables) T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 122 Creating (Declaring) PHP Variables PHP has no command for declaring a variable. A variable is created the moment you first assign a value to it: Example T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 123 Creating (Declaring) PHP Variables After the execution of the statements above, the variable txt will hold the value Hello world!, the variable x will hold the value 5, and the variable y will hold the value 10.5. Note: When you assign a text value to a variable, put quotes around the value. T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 124 PHP is a Loosely Type Language In the example above, notice that we did not have to tell PHP which data type the variable is. PHP automatically converts the variable to the correct data type, depending on its value. In other languages such as C, C++, and Java, the programmer must declare the name and type of the variable before using it. T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 125 PHP Variables Scope In PHP, variables can be declared anywhere in the script. The scope of a variable is the part of the script where the variable can be referenced/used. PHP has three different variable scopes: local global static T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 126 Local and Global Scope A variable declared outside a function has a GLOBAL SCOPE and can only be accessed outside a function. A variable declared within a function has a LOCAL SCOPE and can only be accessed within that function. You can have local variables with the same name in different functions, because local variables are only recognized by the function in which they are declared. The following example tests variables with local and global scope: T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 127 Example Test variables inside the function:"; echo "Variable x is: $x"; echo "
"; echo "Variable y is: $y"; } myTest(); echo "
Test variables outside the function:
"; echo "Variable x is: $x"; echo ""; echo "Variable y is: $y"; ?> T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 128 Local and Global Scope In the example above there are two variables $x and $y and a function myTest(). $x is a global variable since it is declared outside the function and $y is a local variable since it is created inside the function. When we output the values of the two variables inside the myTest() function, it prints the value of $y as it is the locally declared, but cannot print the value of $x since it is created outside the function. Then, when we output the values of the two variables outside the myTest() function, it prints the value of $x, but cannot print the value of $y since it is a local variable and it is created inside the myTest() function. T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 129 PHP The global Keyword The global keyword is used to access a global variable from within a function. To do this, use the global keyword before the variables (inside the function): Example T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 130 PHP The global Keyword PHP also stores all global variables in an array called $GLOBALS[index]. The index holds the name of the variable. This array is also accessible from within functions and can be used to update global variables directly. The example above can be rewritten like this: Example T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 131 PHP The static Keyword Normally, when a function is completed/executed, all of its variables are deleted. However, sometimes we want a local variable NOT to be deleted. We need it for a further job. To do this, use the static keyword when you first declare the variable: T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 132 Example T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 133 Contd.. Then, each time the function is called, that variable will still have the information it contained from the last time the function was called. Note: The variable is still local to the function. T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 134 PHP echo and print Statements There are some differences between echo and print: echo - can output one or more strings print - can only output one string, and returns always 1 Tip: echo is marginally faster compared to print as echo does not return any value. T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 135 The PHP echo Statement echo is a language construct, and can be used with or without parentheses: echo or echo(). Display Strings The following example shows how to display different strings with the echo command (also notice that the strings can contain HTML markup): Example PHP is fun!"; echo "Hello world!
"; echo "I'm about to learn PHP!
"; echo "This", " string", " was", " made", " with multiple parameters."; ?> T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 136 The PHP echo Statement Display Variables The following example shows how to display strings and variables with the echo command: Example "; echo "Study PHP at $txt2"; echo "My car is a {$cars[0]}"; ?> T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 137 The PHP print Statement print is also a language construct, and can be used with or without parentheses: print or print(). Display Strings The following example shows how to display different strings with the print command (also notice that the strings can contain HTML markup): Example PHP is fun!"; print "Hello world!
"; print "I'm about to learn PHP!"; ?> T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 138 The PHP print Statement Display Variables The following example shows how to display strings and variables with the print command: Example "; print "Study PHP at $txt2"; print "My car is a {$cars[0]}"; ?> T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 139 PHP Strings A string is a sequence of characters, like "Hello world!". A string can be any text inside quotes. You can use single or double quotes: Example "; $x = 'Hello world!'; echo $x; ?> T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 140 PHP Integers An integer is a number without decimals. Rules for integers: An integer must have at least one digit (0-9) An integer cannot contain comma or blanks An integer must not have a decimal point An integer can be either positive or negative Integers can be specified in three formats: decimal (10-based), hexadecimal (16-based - prefixed with 0x) or octal (8-based - prefixed with 0) In the following example we will test different numbers. The PHP var_dump() function returns the data type and value of variables: T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 141 Example "; $x = -345; // negative number var_dump($x); echo "
"; $x = 0x8C; // hexadecimal number var_dump($x); echo "
"; $x = 047; // octal number var_dump($x); ?> T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 142 PHP Floating Point Numbers A floating point number is a number with a decimal point or a number in exponential form. In the following example we will test different numbers. The PHP var_dump() function returns the data type and value of variables: T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 143 PHP Floating Point Numbers Example "; $x = 2.4e3; var_dump($x); echo "
"; $x = 8E-5; var_dump($x); ?> T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 144 PHP Booleans Booleans can be either TRUE or FALSE. $x=true; $y=false; T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 145 PHP Arrays An array stores multiple values in one single variable. In the following example we create an array, and then use the PHP var_dump() function to return the data type and value of the array: Example T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 146 PHP Objects An object is a data type which stores data and information on how to process that data. In PHP, an object must be explicitly declared. First we must declare a class of object. For this, we use the class keyword. A class is a structure that can contain properties and methods. We then define the data type in the object class, and then we use the data type in instances of that class: T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 147 Example color = $color; } function what_color() { return $this->color; } } ?> T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 148 PHP NULL Value The special NULL value represents that a variable has no value. NULL is the only possible value of data type NULL. The NULL value identifies whether a variable is empty or not. Also useful to differentiate between the empty string and null values of databases. Variables can be emptied by setting the value to NULL: Example T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 149 PHP String Functions In this chapter we will look at some commonly used functions to manipulate strings. T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 150 The PHP strlen() function The strlen() function returns the length of a string, in characters. The example below returns the length of the string "Hello world!": Example The output of the code above will be: 12 Tip: strlen() is often used in loops or other functions, when it is important to know when a string ends. (i.e. in a loop, we might want to stop the loop after the last character in a string). T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 151 The PHP strpos() function The strpos() function is used to search for a specified character or text within a string. If a match is found, it will return the character position of the first match. If no match is found, it will return FALSE. The example below searches for the text "world" in the string "Hello world!": Example T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 152 The PHP strpos() function The output of the code above will be: 6. Tip: The position of the string "world" in the example above is 6. The reason that it is 6 (and not 7), is that the first character position in the string is 0, and not 1. T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 153 PHP Constants A constant is an identifier (name) for a simple value. The value cannot be changed during the script. A valid constant name starts with a letter or underscore (no $ sign before the constant name). Note: Unlike variables, constants are automatically global across the entire script. T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 154 Set a PHP Constant To set a constant, use the define() function - it takes three parameters: The first parameter defines the name of the constant, the second parameter defines the value of the constant, and the optional third parameter specifies whether the constant name should be caseinsensitive. Default is false. The example below creates a case-sensitive constant, with the value of "Welcome to W3Schools.com!": Example T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 155 Set a PHP Constant The example below creates a case-insensitive constant, with the value of "Welcome to W3Schools.com!": Example T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 156 PHP Arithmetic Operators Operator Name Example Result + Addition $x + $y Sum of $x and $y - Subtraction $x - $y Difference of $x and $y * Multiplication $x * $y Product of $x and $y / Division $x / $y Quotient of $x and $y % Modulus $x % $y Remainder of $x divided by $y T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 157 Example The example below shows the different results of using the different arithmetic operators: T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 158 PHP Assignment Operators The PHP assignment operators is used to write a value to a variable. The basic assignment operator in PHP is "=". It means that the left operand gets set to the value of the assignment expression on the right. T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 159 PHP Assignment Operators Assignme nt Same as... x=y x=y x += y x -= y x *= y x /= y x %= y T2-Lecture-9 Description The left operand gets set to the value of the expression on the right Addition Subtraction Multiplication Division x=x+y x=x-y x=x*y x=x/y x = x % Modulus y Ahmed Mumtaz Mustehsan www.w3schools.com 160 Example The example below shows the different results of using the different assignment operators: T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 161 PHP String Operators Operator . .= T2-Lecture-9 Name Example $txt1 = "Hello" Result Now $txt2 contains Concatenation $txt2 = $txt1 . " world!" "Hello world!" Concatenation $txt1 = "Hello" Now $txt1 contains assignment $txt1 .= " world!" "Hello world!" Ahmed Mumtaz Mustehsan www.w3schools.com 162 Example The example below shows the results of using the string operators: T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 163 PHP Increment / Decrement Operators Operator ++$x $x++ --$x $x-- T2-Lecture-9 Name Preincrement Postincrement Predecrement Postdecrement Ahmed Mumtaz Mustehsan Description Increments $x by one, then returns $x Returns $x, then increments $x by one Decrements $x by one, then returns $x Returns $x, then decrements $x by one www.w3schools.com 164 Example The example below shows the different results of using the different increment/decrement operators: T2-Lecture-9 Ahmed Mumtaz Mustehsan www.w3schools.com 165 The End PHP Part-I Thank You T2-Lecture-9 Mustehsan Ahmed Mumtaz www.w3schools.com 166