DIG1108 Lesson 5


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DIG1108 Lesson 5

  1. 1. INTRO TO SERVER SIDE PROGRAMMING Lesson Five Thursday, September 26, 13
  2. 2. Lists and Dictionaries In computer science, a list (or sequence) is an abstract data type that implements an ordered collection of values. Each instance of a value on a list is usually called an item, entry or element of the list, and if the same value appears multiple times in the list, each is considered a distinct item of the list. An associative array (or dictionary) is an abstract data type composed of a collection of key/value pairs, such that each key appears at most once in the collection. Pairs can be added or removed, and values can be modified or retrieved based on the associated key. Thursday, September 26, 13
  3. 3. What's The Difference? A list is always ordered, can usually return elements or items by numeric index(starting at zero), and might not allow modification of values. A decent implementation of a list should provide specific operations for adding and removing elements to enable them to be used: push - append to the end(or tail) of the list pop - remove from the tail of the list queue(unshift) - append to the beginning(or head) of the list dequeue(shift) - remove from the head of the list A hash is usually not immutable and may be indeterminately ordered. Values can usually be altered. Thursday, September 26, 13
  4. 4. Arrays An array type is a data type that is meant to describe a collection of values or variables, each selected by one or more indices(keys) tha can be computed at run-time of the program. By default, the array type in PHP generates computed, numerical indices, starting with zero, to make a list: var_dump(array( 'one', 'two', 3, 4, 4.1, 4.2 )); $list = array(); $list[] = 'one'; $list[] = 'two'; The value for the key can also be specified as any scalar literal (neither array, object nor resource), often a string var_dump(array( 'one' => 1, 2 => 'two' )): $list[4] = 'four'; $list['five dot one'] = 5.1; Thursday, September 26, 13
  5. 5. Array Tricks PHP relies heavily on arrays, so there are a lot of array- specific functions, like to use an array as a queue or stack array_unshift(), array_shift() - append to and remove from head array_push(), array_pop() - append to and remove from tail PHP arrays have an "internal position" pointer that can be used as an iterator: current(), key() - return the current element or key next(), prev(), end(), reset() - advance forward or back each() - return the current key and value and advance the pointer Thursday, September 26, 13
  6. 6. Even More Array Tricks array_merge() - merge two or more arrays array_slice() - remove an array section array_splice() - insert or replace a section count(), sizeof() - calculate length array_fill(), array_pad(), range() - generate values str_split(), explode(), implode(), join() - array to string Thursday, September 26, 13
  7. 7. ASSIGNMENT 5.1 Find Some Lists and Arrays Thursday, September 26, 13
  8. 8. Lists of Lists Open Github and Cloud 9 Look through your forked projects for examples of lists and dictionary definitions and methods Copy adn paste your examples into a file named "homework-5.1.md" with code delimiters as needed Write comments identifying the lists, keys, indexes and other list and dictionary pieces discussed Save, add and commit, then push to Github when done Thursday, September 26, 13
  9. 9. Recursion Thursday, September 26, 13
  10. 10. Control Flow Statements Control Flow - refers to the order in which the individual statements, instructions or function calls of an imperative or declarative program are executed or evaluated. Execution results in a choice being made as to which of two or more paths should be followed. Types of Control Flow statements: continuation at a different statement (unconditional branch or jump) execute statements only if some condition is met (conditional branch) execute statements until some conditional is met(loop, conditional branch) execute defined statements and return (sub/co-routines, continuations)s stop executing statements (unconditional halt) Thursday, September 26, 13
  11. 11. Loops A loop is a sequence of statements which is specified once but which may be carried out several times in succession, a specified number of times or indefinitely Specific number of times: for ( $count = 0; $count < $max; $count++ ) do_something(); Once per each item in a collection(array): foreach ( $collection as $item ) do_something(); foreach ($collection as $key => $value ) do_something(); Until some condition is met: while ( $condition == true ) do_something(); do something(); while ( $condition ); Indefinitely(infinitely): while ( true ) do_something(); do something(); while ( true); Thursday, September 26, 13
  12. 12. Infinite Loops An unconditional(or infinite) loop returns to a fixed point in the diagram, usually the top of the workflow. Without a breaking statement or escape clause, it executes forever. Thursday, September 26, 13
  13. 13. Conditional Loops A conditional loop (while, do-while, for, foreach) returns to a condition check ($count < $max). Until the condition evaluates FALSE, the loop will continue to execute Thursday, September 26, 13
  14. 14. Diagramming Part Two In your pair, find a section of a project that has some significant looping and conditional logic (at least three branches) Individually, sketch a simple workflow diagram of the logic; assemble a truth table if needed Discuss differences in your diagrams and make a new diagram and truth table for the logic to demonstrate Thursday, September 26, 13
  15. 15. ASSIGNMENT 5.2 Loops and Conditionals Thursday, September 26, 13
  16. 16. Create a file called "homework-5.2.md" in your "assignments" workspace on Cloud 9 Find a section in your projects that has some decent looping and branching code: at least five branches that you can diagram. Copy and paste your example into your file and attempt to identify the loop conditions with comments: while ( $count < $max ) { // while $count is less than $max foreach ( $collection as $item ) { // until there are no more $items in the $collection Save your file, then git add, git commit -m "explain why" and git push Thursday, September 26, 13