PHP Quick Intro

VARIABLES

• Start with a dollar sign,for example : $variable_name=2;
• Do not need to be declared before use.
• Can hold a string, or a number, or a boolean: $a="cat"; $b=42; $c=false;
• Can store floating point numbers: $b=42.06;

STRINGS

• Can be assigned to a variable: $w = "world";
• Can be concatenated with the period (.) operator: "hello ".$w yields "hello world"
• The concatenation operator is used a lot. Remember it.
• You can get the length: strlen($w) returns 5
• You can get a substring: substr($w,1,3); returns orl
• Can be operated on by many PHP built in string functions
• Can be enclosed by double quotes (") or single quotes ('): $w = 'world';
• There are differences between single and double quotes.
• In double quotes, you can embed variables: "hello $w" produces hello world - the variable is substituted (its name replaced by its value)
• But if you try that with single quotes: 'hello $w' produces hello $w
• That same idea applies to special chars: "hello\n" produces a newline
• But 'hello\n' produces hello\n as a string (no newline) - taken literally with no substitution
• You can put a double quote in a double quoted sting by escaping: "Hello \"World\"" produces Hello "World"
• PHP strings act very differently than C character arrays. Much simpler to work with.

ARRAYS

• Create an empty one like this: $myarray=array();
• Create one with some elements: $myarray=array("cat","dog","hamster");
• Can hold a mixture of data types: $myarray=array("cat",42,false);
• Start with index of 0: echo $myarray[0]; // outputs: cat
• Unless the keys are specified: $myarray=array(1=>"cat",2=>42);
• And the keys don't have to be numbers, they can be strings: $myarray=array("fluffy"=>"cat","rover"=>"dog");
• Can append to an array like this: $myarray[]="a new element"
• Find out how many elements it has: count($myarray)
• Sort the array: sort($myarray)
• Sort the array by keys instead of values: ksort($myarray)
• Can be operated on by many built in PHP array functions.

FROM STRING TO ARRAY AND BACK AGAIN

• Here's a string: $s="Cat,Dog,Cow,Pig"
• Create an array from it: $a=explode(',',$s);
• $a[0] is now Cat, $a[3] is Pig
• Let's overwrite the Pig: $a[3]="Goose";
• Go back to a string: $s=implode(',',$a);
• $s is now: "Cat,Dog,Cow,Goose"

LOOPING

• foreach loops through entire arrays:
  

  $myarray=array("fluffy"=>"cat","rover"=>"dog");
    foreach ($myarray as $element) {
      echo $element;
    }
    // Outputs: cat, dog
  

• But you can also get at the array key values:
  

  $myarray=array("fluffy"=>"cat","rover"=>"dog");
    foreach ($myarray as $k => $element) {
      // We're using the concatenation operator here (period, remember?)
      echo $k." is a ".$element;
    }
    // Outputs: fluffy is a cat, rover is a dog
  

• There are other ways to loop, but foreach covers 90% of what you'll ever need.

IF-ELSE

• Looks just like if-else in C and other languages.
• Optionally, you can use a colon and endif statement, instead of braces:
  

  // using curly braces:
    if ($w=="world") {
      echo "hello ".$w;  // aside: note the concatenation operator (period)
    }
    // This is the same logic:
    if ($w=="world):
      echo "hello $w";  // aside: this time we didn't use concatenation!
    endif;
  

• There is a tertiary operator: echo ($w=="world") ? "hello $w" : "goodbye";

MIXING PHP WITH HTML

• Files ending with .php contain HTML and PHP
• PHP must be enclosed within PHP tags: <?php echo "I'm PHP";?>
• If it's not within PHP tags, it gets sent to the Browser unaltered.
• So whatever is not within PHP tags should be valid HTML/CSS/Javascript
• You can use the short PHP tag: <? echo "I'm PHP";?>
• For an echo, this is most concise: <?="I'm PHP"?>
• Works well for variables: <div class="<?=$classname?>">