Tutorial 2 : Variables Variables A variable is a special container that you can define to "hold" a value. A variable consists of a name that you can choose, preceded by a dollar ($) sign. The variable name can include letters, numbers, and the underscore character (_). Variable names cannot include spaces or characters that are not alphanumeric. The following code defines some legal variables: $a; $a_longish_variable_name; $2453; $sleepyZZZZ; Remember that a semicolon (;) is used to end a PHP statement. The semicolons in the previous fragment of code are not part of the variable names. NOTE: PHP do not have data types for the variables, that’s because it is a loosly typed language and it correctly assign a data type for the variables according to the use of the variable. <?php $num1 = 10; //this variable is Integer $num2 = 20; //this is same too Print $num1+$num2; ?> <?php $name = “PHP 4”; //this variable is String Print $name; ?> <?php $num = 123.456; //this variable is double Print $num/12; ?> Data Types Different types of data take up different amounts of memory and may be treated differently when they are manipulated in a script. Some programming languages therefore demand that the programmer declare in advance which type of data a variable will contain. PHP4 is loosely typed, which means that it will calculate data types as data is assigned to each variable. This is a mixed blessing. On the one hand, it means that variables can be used flexibly, holding a string at one point and an integer at another. On the other hand, this can lead to confusion in larger scripts if you expect a variable to hold one data type when in fact it holds something completely different. The gettype() function You can use PHP4's built-in function gettype() to test the type of any variable. If you place a variable between the parentheses of the function call, gettype() returns a string representing the relevant type. <?php $number = 123; $num = 123.456; $name = "PHP 4"; Print "Using gettype()<br>"; Print gettype($number)."<br>"; Print gettype($num)."<br>"; Print gettype($name); ?> This will print as follows, Using gettype() Intrger Double String Changing Type with settype() PHP provides the function settype() to change the type of a variable. To use settype(), you must place the variable to change (and the type to change it to) between the parentheses and separated by commas. <?php $var = 12; //integer Print gettype($var).”<br>”; //integer Settype($var , double); Print gettype($var) .”<br>”; //double Settype($var , string); Print gettype($var) .”<br>”; //string Settype($var , boolean); Print gettype($var); //boolean ?> Changing Type by Casting By placing the name of a data type in brackets in front of a variable, you create a copy of that variable's value converted to the data type specified. The principal difference between settype() and a cast is the fact that casting produces a copy, leaving the original variable untouched. <?php $var = 10; Print gettype($var); //integer $var1 = (double)$var; Print gettype($var1); //double $var2 = (string)$var; Print gettype($var2); //string ?> The Assignment Operator You have met the assignment operator each time we have initialized a variable. 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 ="matt"; The variable $name now contains the string "matt". Interestingly, this construct is an expression. It might look at first glance that the assignment operator simply changes the variable $name without producing a value, but in fact, a statement that uses the assignment operator always resolves to a copy of the value of the right operand. Thus print ( $name = "matt" ); prints the string "matt" to the browser in addition to assigning "matt" to $name. Arithmetic Operators The arithmetic operators do exactly what you would expect. The addition operator adds the right operand to the left operand. Thesubtraction operator subtracts the right-hand operand from the left. The divisionoperator divides the left-hand operand by the right. The multiplication operator multiplies the left-hand operand by the right. The modulus operator returns the remainder of the left operand divided by the right.
The Concatenation Operator The concatenation operator is a single dot. Treating both operands as strings, it appends the right-hand operand to the left. So "hello"." world" returns "hello world" Regardless of the data types of the operands, they are treated as strings, and the result always is a string. More Assignment Operators Although there is really only one assignment operator, PHP4 provides a number of combination operators that transform the left-hand operand as well as return a result. As a rule, operators use their operands without changing their values. Assignment operators break this rule. A combined assignment operator consists of a standard operator symbol followed by an equals sign. Combination assignment operators save you the trouble of using two operators yourself. For example, $x = 4; $x += 4; // $x now equals 8 is equivalent to $x = 4; $x = $x + 4; // $x now equals 8 There is an assignment operator for each of the arithmetic operators and one for the concatenation operator.
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