PHP Programming Flashcards

Question 1

What does the name PHP stand for in its current form?

Accepted Answer

PHP stands for PHP: Hypertext Preprocessor, a recursive acronym whose name originally referred to Personal Home Pages. It is an open source scripting language built mainly for server side web development. Its code runs on the web server, and the browser receives only the generated output, usually HTML.

Question 2

How do PHP code blocks begin and end inside an HTML file?

Accepted Answer

PHP code inside an HTML file is enclosed between the opening tag and the closing tag. The opening tag is the less than sign followed by a question mark and the word php, and the closing tag is a question mark followed by the greater than sign. Text outside these tags is sent to the browser unchanged.

Question 3

How is a PHP statement terminated, and why does that rule matter?

Accepted Answer

Each PHP statement normally ends with a semicolon, which tells the interpreter where one instruction stops and the next begins. Forgetting the semicolon is one of the most common causes of parse errors, because the interpreter may read the next line as part of the same statement.

Question 4

How does echo differ from print in PHP?

Accepted Answer

Both echo and print send text to the output. Echo is a language construct that can take several comma separated arguments and does not return a value. Print is also a construct but accepts only one argument and always returns the integer one, so it can be used inside expressions.

Question 5

What are the main comment styles in PHP, and what do they do?

Accepted Answer

PHP supports single line comments that begin with two forward slashes or a hash symbol, and multiline comments that begin with a slash and asterisk and end with an asterisk and slash. The interpreter ignores all comment text, so comments explain code to people without changing what it does.

Question 6

What is the purpose of the php.ini configuration file?

Accepted Answer

The php.ini file holds configuration settings that control how the PHP engine behaves, such as error reporting, upload size limits, and default time zone. Its location depends on how PHP was installed, and the phpinfo function can show which file is loaded. Changes usually take effect after the web server or PHP process restarts.

Question 7

How does running PHP from the command line differ from serving it through a web server?

Accepted Answer

A script run from the command line sends its output to the terminal and reads input from the keyboard or arguments, while a script served by a web server sends its output as the body of an HTTP response. Headers must be sent before any output in web mode.

Question 8

What is the difference between a PHP warning and a fatal error?

Accepted Answer

A warning reports a problem that does not stop the script, such as using an undefined variable, so execution continues after it. A fatal error stops the script immediately, for example when calling a function that does not exist. Both are shown according to error reporting settings.

Question 9

How do you declare a variable in PHP, and what prefix does it need?

Accepted Answer

Every PHP variable begins with a dollar sign followed by a name, and the name must start with a letter or underscore. You do not declare a type in advance, and assigning a value with the equals sign creates the variable. Case matters for variable names, so count and Count are different.

Question 10

What are the main scalar data types in PHP?

Accepted Answer

The four scalar types are integer, float, string and boolean. Integers are whole numbers, floats are numbers with decimal points, strings hold text in quotes, and booleans hold either true or false. PHP also has array, object, resource and null types, but the four scalar types cover most everyday values.

Question 11

How does PHP's loose comparison differ from strict comparison?

Accepted Answer

The loose equality operator, written with two equals signs, converts operands to a comparable type before checking them, so the integer 1 and the string 1 are considered equal. Strict comparison with three equals signs checks both value and type, so no conversion happens and those two values are not identical.

Question 12

What does the dot operator do with strings in PHP?

Accepted Answer

The dot operator joins two strings into one, a process called concatenation. For example, a first name and a last name can be joined with a space between them. PHP also provides the concatenation assignment operator, written as a dot followed by an equals sign, which appends text to an existing variable.

Question 13

What does the null coalescing operator do in PHP?

Accepted Answer

The null coalescing operator, written as two question marks, returns its left operand when that value exists and is not null, and otherwise returns the right operand. It suits default values, such as a missing form field. It does not raise a warning for an undefined variable or array key.

Question 14

How can you explicitly convert a value to another type in PHP?

Accepted Answer

You convert a value by placing a cast in parentheses before it, such as the int cast for integers or the string cast for text. The intval and strval functions do the same job when a function call reads more clearly. Explicit casts make the intended type visible to anyone reading the code.

Question 15

Which operators give the remainder and the power of numbers in PHP?

Accepted Answer

The percent sign is the modulus operator, which returns the remainder after division, so 10 % 3 gives 1. The double asterisk is the exponentiation operator, so 2 ** 3 gives 8. Both follow the usual precedence rules, and parentheses make the intended order clear.

Question 16

How does a constant differ from a variable in PHP code?

Accepted Answer

A constant is a named value that cannot change once it has been defined, while a variable can be reassigned as a script runs. Constants are defined with the define function or the const keyword, and they do not use a leading dollar sign.

Question 17

How does an if statement with elseif and else choose a branch?

Accepted Answer

An if statement runs its block only when its condition evaluates to true. If that condition is false, PHP checks each elseif condition in order and runs the first block whose condition is true. If no condition matches, the else block runs, if one is present. Only one branch of the chain executes.

Question 18

How does a switch statement differ from a chain of if statements?

Accepted Answer

A switch statement compares one expression against several case values and runs the code for the first match. Each case usually ends with a break statement, because without it execution falls through into the next case. A chain of if statements can test different conditions, while switch is designed for matching a single value.

Question 19

What distinguishes a while loop from a do while loop in PHP?

Accepted Answer

A while loop checks its condition before each pass, so the body may run zero times if the condition starts false. A do while loop runs its body once first and then checks the condition, which guarantees at least one execution. Both loops need a change inside the body so the condition becomes false.

Question 20

How does a foreach loop step through the elements of an array?

Accepted Answer

A foreach loop walks through each element of an array in order, assigning the current value to a loop variable on every pass. It can also provide the key when written with a double arrow, which is helpful for associative arrays. The loop ends automatically after the last element, so no counter is needed.

Question 21

How do you define a function in PHP and then call it?

Accepted Answer

You define a function with the function keyword, followed by a name, a parameter list in parentheses, and a block of code. You call it by writing its name followed by parentheses, passing arguments that match the parameters in order. A function can return a value using the return keyword.

Question 22

What are default parameter values, and how do they work in functions?

Accepted Answer

A default parameter value is used when the caller does not supply an argument for that parameter. It is written with an equals sign after the parameter name, such as a greeting parameter. Parameters with defaults should appear after required parameters, because PHP fills arguments from left to right.

Question 23

How can a PHP function modify a variable that was passed to it?

Accepted Answer

Place an ampersand before the parameter name in the function definition, so the function receives a reference to the caller's variable rather than a copy. Any change the function makes to that parameter then affects the original variable after the call. Use this only when modification is intended.

Question 24

What is variable scope, and how does it affect functions in PHP?

Accepted Answer

Variable scope determines where a variable can be accessed. A variable created inside a function is local to that function and disappears when the function finishes. Variables defined outside a function are not automatically visible inside it, so they must be passed as arguments or brought in with the global keyword.

Question 25

How does an indexed array differ from an associative array in PHP?

Accepted Answer

An indexed array stores values under automatic numeric positions that start at zero, while an associative array stores values under named keys chosen by the programmer. Both kinds are created with the array construct or short square bracket syntax, and the difference lies only in the keys used.

Question 26

How do you add, read, and remove individual elements in a PHP array?

Accepted Answer

You add an element by assigning a value to a new key, or by using empty square brackets to append to an indexed array. You read an element by writing its key in square brackets, and you remove one with the unset function. Removing an element does not renumber the remaining keys.

Question 27

Which functions count array elements and check whether a key exists?

Accepted Answer

The count function returns the number of elements in an array. The array_key_exists function tells you whether a key is present, while isset also reports false for keys holding null. Checking first avoids warnings and lets code handle missing data cleanly.

Question 28

How do sort, asort, and ksort differ when ordering a PHP array?

Accepted Answer

The sort function reorders the values of an array and reindexes the keys from zero, while asort keeps each key paired with its value. The ksort function sorts by key instead. Each of these functions changes the array in place and returns true on success rather than a new sorted copy.

Question 29

How do the explode and implode functions work with strings in PHP?

Accepted Answer

The explode function splits a string into an array of pieces using a chosen separator, such as a comma. The implode function does the reverse, joining array elements into one string with a glue string placed between them. Together they are handy for processing comma separated data.

Question 30

How do single quoted and double quoted strings differ in PHP?

Accepted Answer

Single quoted strings take their content literally, so almost no characters are interpreted, apart from escaping a single quote or backslash. Double quoted strings interpolate variables and recognize escape sequences such as newline. For example, a variable name written inside double quotes is replaced by its value.

Question 31

Which PHP functions measure string length and change letter case?

Accepted Answer

The strlen function returns the number of bytes in a string, which equals the number of characters only for single byte text. The strtolower and strtoupper functions convert letters to lower or upper case. For multibyte text such as accented characters, the mb_ functions from the mbstring extension handle characters correctly.

Question 32

How can you search for text in a PHP string and replace part of it?

Accepted Answer

The strpos function returns the position of the first match or false if the text is not found, so comparisons should use strict false checks. The str_replace function replaces every occurrence of a search string with a replacement string. Both functions are case sensitive, while str_ireplace and stripos offer case insensitive versions.

Question 33

What are the superglobal arrays $_GET and $_POST used for in PHP?

Accepted Answer

The $_GET array holds values sent in the URL query string. The $_POST array holds values sent in the body of an HTTP POST request, which is typical for submitted form data. Both are associative arrays keyed by the names of the form fields or parameters.

Question 34

Why should user input be validated and sanitized before a PHP program uses it?

Accepted Answer

User input can contain unexpected or malicious content, so it should be checked before the program relies on it. Validation confirms that a value has the expected form, such as a whole number within a range or a properly formatted email address. Never trust input merely because a form appears to restrict it, since clients can send any data they like.

Question 35

How does a PHP script receive data from a form submitted with POST?

Accepted Answer

The form element sets its method attribute to post, and each input field's name becomes a key in the $_POST array. In the script, you check the request method and read values such as $_POST followed by the field name in square brackets. Reading a field that was not sent should be avoided without checking first.

Question 36

What is a PHP session, and how do you start one?

Accepted Answer

A session stores data for one visitor across multiple page requests, which HTTP does not remember by itself. You begin one by calling the session_start function before any output is sent, and then read or write values through the $_SESSION array. The server links each visitor to stored data using a session identifier.

Question 37

How can you safely display user supplied text inside an HTML page?

Accepted Answer

Use the htmlspecialchars function to convert special characters such as the less than sign, the ampersand, and quotation marks into HTML entities before echoing the text. This prevents browsers from interpreting submitted content as markup, which is the main defense against cross site scripting.

Question 38

How can a PHP program use a database safely to prevent SQL injection?

Accepted Answer

Use prepared statements through PDO or MySQLi, which send the query structure separately from the values supplied by the user. Placeholders such as named or question mark markers stand in for the values, and the database treats bound values as data rather than as SQL code.

Question 39

What do password_hash and password_verify do, and why are they used?

Accepted Answer

The password_hash function creates a one way hash of a password using a strong algorithm, and password_verify checks a login attempt against that hash. Storing hashes rather than plain text means a leaked database does not directly reveal user passwords. Never store passwords with reversible encryption or fast general purpose hashes alone.

Question 40

How should a production PHP site handle errors so that visitors see no sensitive details?

Accepted Answer

In production, display_errors should be turned off so visitors do not see file paths, stack traces, or database details. Errors should instead be written to a log file, which developers can review privately. Wrapping risky operations in try and catch blocks lets the program respond with a friendly message instead of crashing.

PHP Programming Flashcards

1PHP basics and syntax

2Variables, types and operators

3Control flow and functions

4Arrays and strings

5Web requests and security

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