1. Web Database Programming Week 3 PHP (2)

2. Functions Group related statements together to serve “a” specific purpose –Avoid duplicated code –Easy maintenance of code No need to change multiple places Built-in functions –E.g. print(), phpinfo() –Use PHP manual to look up existing functions –Do not reinvent the wheel User defined functions

3. Function Definition Define a function –“function” keyword –Function name –Parameters (input) –Function body (the real work) –Return statement (output) E.g. a function to make a string display in Bold

4. Use a function Call the function –Invoke the function by use its name, and –Pass in the values for parameters –Must match the function definition –The value of a function is its return value

5. Variable Scope Variables defined inside a function (including the parameters) are limited to use within the function only –They are undeclared (invisible) outside the function –A new variable with the same name will be created if it appears outside the function body –They disappear when the function exits Variables defined outside a function is global, visible throughout the file Scopes are nested –Inner scope take precedence

6. Exceptions Global statement indicates a variable is global –A global variable can be used inside a function Static statement indicates a variable is static –Does not lose value after the function exits –E.g. a variable that count how many times a function is called.

7. Passing arguments into function Default is to pass by value –Only the value of a variable is passed in (copy), the original variable does not change PHP support pass by reference –The reference (address) to the variable is passed in, so the original variable can be changed by the function –Prefix with an ampersand character “&” –PHP also support assignment by reference Default argument value –The argument can then be omitted in function call

8. Array An ordered set of variables (elements) –Pairs of key => value –Allow random access by key –Key can be integers (default) or string –Value can be any type, even array Define array: array() Access an array element: array_expression[key]

9. More Array Using unset() to delete an array or an array element The order of array elements is by the order of them entering the array Multidimensional array –An element can itself be an array –Access each dimension with an extra [] Using foreach(array_expression as $key => $value) to loop through array

10. Some Array Functions Number of elements: count() Instances of each value: array_count_values() Create array with values: array_fill(), range() Break up a string into an array: explode() Search in array : in_array(), array_key_exists() Sort: sort()

11. String Manipulations Nth character of a string: $aString{n} Length: strlen() Change case : strtolower(), strtoupper() Trimming whitespace : ltrim(), rtrim(), trim() Compare : strcmp() Substring : substr() Search in string : strpos(), strstr() Replace substring: substr_replace()