PHP Interview questions

By November 12, 2011 PHP

1.  Would you initialize your strings with single quotes or double quotes?
– Since the data inside the single-quoted string is not parsed for variable substitution, it’s always a better idea speed-wise to initialize a string with single quotes, unless you specifically need variable substitution.
2. How come the code <?php print “Contents: $arr[1]”; ?> works, but <?php print “Contents: $arr[1][2]”; ?> doesn’t for two-dimensional array of mine?
 – Any time you have an array with more than one dimension, complex parsing syntax is required. print “Contents: {$arr[1][2]}” would’ve worked.

3. What is the difference between characters 23 and x23?
– The first one is octal 23, the second is hex 23.
4.  I want to combine two variables together:
 $var1 = ‘Welcome to ‘;
 $var2 = ‘TechInterviews.com’;
       $var 3 = $var1.$var2;
5.  For printing out strings, there are echo, print and printf. Explain the differences.
 – echo is the most primitive of them, and just outputs the contents following the construct to the screen. print is also a construct (so parentheses are optional when calling it), but it returns TRUE on successful output and FALSE if it was unable to print out the string. However, you can pass multiple parameters to echo, like:
 <?php echo ‘Welcome ‘, ‘to’, ‘ ‘, ‘TechInterviews!’; ?>
and it will output the string “Welcome to TechInterviews!” print does not take multiple parameters. It is also generally argued that echo is faster, but usually the speed advantage is negligible, and might not be there for future versions of PHP. printf  is a function, not a construct, and allows such advantages as formatted output, but it’s the slowest way to print out data out of echo, print and printf.
6.  I am writing an application in PHP that outputs a printable version of driving directions. It contains some long sentences, and I am a neat freak, and would like to make sure that no line exceeds 50 characters. How do I accomplish that with PHP?
– On large strings that need to be formatted according to some length specifications, use wordwrap() or chunk_split().
7.  What’s the output of the ucwords function in this example?
        $formatted = ucwords(“INTERVIEW QUESTIONS”);
        print $formatted;
What will be printed is INTERVIEW QUESTIONS.

ucwords() makes every first letter of every word capital, but it does not lower-case anything else. To avoid this, and get a properly formatted string, it’s worth using strtolower() first.
·  What’s the difference between htmlentities() and htmlspecialchars()?
– htmlspecialchars only takes care of <, >, single quote ‘, double quote ” and ampersand. htmlentities translates all occurrences of character sequences that have different meaning in HTML.
8.  What’s the difference between md5(), crc32() and sha1() crypto on PHP?
 – The major difference is the length of the hash generated. CRC32 is, evidently, 32 bits, while sha1() returns a 128 bit value, and md5() returns a 160 bit value. This is important when avoiding collisions.
9.  So if md5() generates the most secure hash, why would you ever use the less secure crc32() and sha1()?
– Crypto usage in PHP is simple, but that doesn’t mean it’s free. First off, depending on the data that you’re encrypting, you might have reasons to store a 32-bit value in the database instead of the 160-bit value to save on space. Second, the more secure the crypto is, the longer is the computation time to deliver the hash value. A high volume site might be significantly slowed down, if frequent md5() generation is required.
10.  What does a special set of tags <?= and ?> do in PHP?
– The output is displayed directly to the browser.
11.  What’s the difference between include and require?
It’s how they handle failures. If the file is not found by require(), it will cause a fatal error and halt the execution of the script. If the file is not found by include(), a warning will be issued, but execution will continue.
12.  I am trying to assign a variable the value of 0123, but it keeps coming up with a different number, what’s the problem?
 – PHP Interpreter treats numbers beginning with 0 as octal.
13. Would I use print “$a dollars” or “{$a} dollars” to print out the amount of dollars in this example?
In this example it wouldn’t matter, since the variable is all by itself, but if you were to print something like “{$a},000,000 mln dollars”, then you definitely need to use the braces.
14.  How do you define a constant?
 – define() directive, like define (“MYCONSTANT”, 100);
15.  How do you pass a variable by value in PHP?
– Just like in C++, put an ampersand in front of it, like $a = &$b
16.  Will comparison of string “10” and integer 11 work in PHP?
– Yes, internally PHP will cast everything to the integer type, so numbers 10 and 11 will be compared.
17.  When are you supposed to use endif to end the conditional statement?
– When the original if was followed by : and then the code block without braces.
18.  Explain the ternary conditional operator in PHP?
– Expression preceding the ? is evaluated, if it’s true, then the expression preceding the : is executed, otherwise, the expression following : is executed.