2. Language Basics Flashcards
What does Lexical Structure mean?
Set of basic rules that governs how you write in that language.
Which constructs are case-insensitive, and which are case-sensitive?
Case Insensitive – Classes & functions as well as built-in constructs and keywords.
Case Sensitive – Variables.
Is PHP Whitespace sensitive?
No, generally semi-colon is used for ends of lines and whitespace isn’t taken into account.
What are the multiple types of comments in PHP?
Single Line
- //
- #
Multi Line
- /* */
What are the legal identifiers for variables?
Must begin with a dollar sign, first character must be ASCII letter (upper or lower) or an underscore. After the first character, 0-9 are also valid characters.
Valid
$bill
$head_count
$I_HEART_PHP
$_secret
Invalid
$not valid
$*w
$3a
How do you define/use a constant?
Need to call the define(‘CONST_NAME’, ‘VALUE) function. Can be used from then on my referring to it by name.
What are Keywords in PHP?
Reserved words for the languages core functionality. They are case insensitive and can’t be used for variables/classes defined by the user.
What are the data types in PHP?
Scalar Types
- integer
- floating-point
- string
- boolean
Compound Types
- arrays
- objects
How do you define an Octal number in PHP?
Start an integer with a leading 0, and a series of digits 0-7.
How do you define a Hexadecimal value in PHP?
Prefix an integer with 0x followed by digits 0-9 or letters A-F.
How do you define a Binary value in PHP?
Write an integer value that begins with 0b followed by a sequence of 0-1.
What happens if you try to store a value that’s too big to hold an integer?
It will automatically convert to a floating-point value.
How can we test if a value is an integer?
Use the is_int() function.
Floating point values are only approximations, with that in mind how can we test if floats are equal?
Convert them to integers for comparison
How can you test if a value is a float?
Use the function is_float();
What’s the difference between single and double quoted strings in PHP?
Single quotes – String literals, they will not be interpolated.
Double quotes – Strings will be interpolated before returning value. (Variables will be expanded)
How can you test if two strings are equal?
Simply use == operator.
How can you test if a variable is a string in PHP?
Use the is_string() function
Booleans represent a truth value, what all values evaluate to false?
- keyword ‘false’
- integer 0
- floating-point 0.0
- empty string “” AND string “0”
- Empty array []
- the value NULL
How can we test if a value is a boolean?
use the is_bool() function
What are the 2 ways of creating an array in PHP?
using the array(“”) construct or the shorthand []
What are the 2 ways we can use a foreach loop with an array?
We can do foreach ($array as $value) OR foreach ($array as $index => $value) depending on if we need the index or not.
How can we determine if a variable is an array?
Use the is_array() function
How do we define a class?
Using the class keyword.
How do we create a new object from a class?
Use the new keyword. You can optionall pass parameters to the constructor if needed as well, or you can omit the parenthesis entirely.
How can you access the methods/properties of an object?
Use the -> (Arrow) construct.
How can you test if something is an object?
Use the is_object() function.
How can you test if a value is a Resource or not?
Use the is_resource() function.
How can you test if a value is NULL?
Use the is_null() function
How can you create a pointer/alias to another variable?
Use the =& operand.
How can we destroy a pointer/alias without changing the underlying value?
Use the unset() function.
What’s the syntax for getting a function return value by reference? What’s special about the assignment?
You need to use the & operator in front of the function name. You also need to use reference assignment when assigning to a variable, else PHP will use the value and not the actual reference.
What’s the scope of variables declared outside of a function? Are they available within a function?
They’re global scope, and aren’t accessible within a function. They’re available from any part of a program, but not within functions.
How can you access a global variable within a function?
Use the global keyword to ‘pull it into the function’.
What’s special about static variables within functions?
They retain their value between calls to the function, but are only visible within that function.
What are the 2 ways PHP managed memory?
Reference counting – Ensures memory is returned to OS when it’s no longer needed (not referenced anywhere)
copy-on-write – When copying a value from on variable to another, PHP doesn’t get more memory. Instead it updates the symbol table to indicate both are using the SAME chunk of memory. Subsequently if we modify one of our values it will NOW copy, since we’re modying it. (See image for example)
How can you see if a variable is set to any value?
Use the isset() method.
If you wanted to destroy a variable (and remove it from the symbol table) how would you do that?
Use the unset() function. If you set it to NULL, this will destroy the value but it’s still a defined variable according to PHP.
In regard to type juggling, how are Strings converted to integers?
The string is presumed to start with a number, if no number is found at the start it’s set to 0.
If the String contains a ‘.’ or ‘E’ or ‘e’ it will be evaluated as a floating-point value. Int he case of ‘e/E’ it will assume scientific notation.
What’s the syntax for Exponentiation?
$base ** $exponent
How do you do String concatenation?
‘String part ‘ . $var1 . ‘ ending part’
What’s the difference in both syntax and logic for pre-increment vs post-increment? Same question for decrement operator.
Post-Increment/Decrement – Returns the value as it exists at that moment, then increments the value. Place the ++ or – AFTER the variable. $var++
Pre-Increment/Decrement – Returns the value AFTER doing the increment or decrement. Place the ++ or – BEFORE the variable. –$var
What is the Spaceship operator? What does it do?
<=>
It does a comparison to left and right hand operands.
Equal => 0
Left greater => -1
Right greater => 1
What is the Null Coalescing operator? What does it do?
??
Operator check if lefthand operand is not null, if not it uses that. Else evalutes righthand operand.
What does casting an object to an array do?
Builds an array of properties of the object.
What happens if you cast an array to an object?
You build an object whose properties correspond to the array’s keys and values.
What does the assignment operator look like? What does it do?
=
Assigns values to variables. It also returns the value that was just assigned.
What does the instanceof operator do? How is it useful?
$a instanceof Person
Returns true/false. Test whether a variable of an instantiated object is of a given class or implements an interface. Useful to test if an object implements an interface.
What is the alternative syntax for an if statement?
What is the alternative syntax for control structures such as loops/if useful for?
Mixing in PHP with HTML. You can in a much cleaner way mix the two without echo for a ton of html.
What’s the syntax for a switch statement? What is a gotcha for them?
Start with switch ($var) then list your cases, making sure to break all statements as PHP does fall-through. Can leave default statement as catch-all.
What does putting a number after a break or a continue statement do?
Determines how many levels of structures to break out of, or loop to continue for.
How do you leave the entire application in PHP?
exit() or die()
You can also specify a message, which will be printed before exiting.
What’s the echo short tag? What’s the availability of this tag?
With this tag you don’t need the echo.
This tag is avaiable at all times.
