Web Database Programming Week 3

1. Web Database ProgrammingWeek 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()