ITEC 325 2011spring ibarland

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ch06
conditionals, loops
chapter 6, flow control

From PHP Visual Quickstart Guide by Larry Ullman
Based on notes by Jack Davis (jcdavis@radford.edu)

• if statements

  • if (condition) { statement… } else { statement… }

  • elsif

    if (condition) { statement… } elsif (condition) { statement… }… else { statement… }

• Remember: PHP boolean values true, false
• Validation Functions
  • empty() function
    This is similar to just using the value as a boolean, and to to /or casting to bool. (It may be more readable, especially for known strings.)
    returns TRUE if parameter has value other than 0 or the empty string
    
    $v1 = 0; $v2 = 'something';
    empty($v1); // returns FALSE
    empty($v2); // returns TRUE
    
  • isset() function
    returns TRUE if a variable has a value (including 0 or an empty string)
    
    isset($v1); // returns TRUE
    isset($v3); // returns FALSE
    isset($v1,$v3); // returns FALSE
  • isnumeric() function
    returns TRUE if a variable has a numeric value
    isnumeric($v1); # returns TRUE
    isnumeric($v2); # returns FALSE
    
  • checkdate() function
    returns TRUE, if the date exists
    checkdate(1,7,2010); // returns true
• Comparison Operators
  • ==    # is equal
  • !=    # not equal
  • ===    # is identical to (no coercion)
  • !==    # is not identical to (no coercion, so '4' is not equal to 4)
  • <, <=    # lt, lt or equal
  • >, >=    # gt, gt or equal
  • !    # not
  • AND,&&    # boolean AND
  • OR,||    # boolean OR
  • XOR    # boolean exclusive or
• The Switch Conditional A different way of writing if-elsif-else statements:

  switch ($someLongExpr) { case 'value1': statement… break; case 'value2': statement… break; default: statement… break; }

  The temptation is to write this so that you don't need to keep writing if ($someLongExpr == 'valuen'). but putting it in a short variable name and using if-elsif-else has many advantages:

  $v = $someLongExpr; if ($v == 'value1') { statement… } elsif ($v == 'value2') { statement… } else { statement… }

  This approach is always fewer characters than the equivalent switch; it's not as prone to extremely-hard-to-track-down bugs like forgetting a break; it's possible to compare with (say) ===, strcasecmp, etc.. (Admittedly, it's also possible to have more complicated conditions where the order of the cases matters.¹)
• while and do-while loops:
  

  while (condition) { statement… } do { statement… } while (condition);

• for loops
  

  for ( initStmt; condition; endOfLoopUpdateStmt ) { statement… }

• break, continue, exit, die
  

  break exits the nearest control structure (if, for, …)
  continue (for loops only): jumps to the start of the next loop iteration.
  If you need to use break or continue, consider re-writing your code/loops to exit naturally. (If somebody reads your code and sees “while(i < 10 && !badInputFound)”, they'll presume that the condition shows how the loop will end; it's only error-prone to have additional ways of exiting the loop. It's often just a matter of adding a boolean flag, and besides in real life that flag is often still helpful in the lines following the loop, to check how the loop exited.)

  exit, die — terminate execution of the PHP program
     can be called with an error message: e.g. die("Fatal Error");

• ch06-flow-control-form.php

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©2011, Ian Barland, Radford University Last modified 2011.Apr.10 (Sun)

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