Job interview Questions in PHP

What Are the Special Characters You Need to Escape in Single-Quoted Stings?

There are two special characters you need to escape in a single-quote string: the single quote (') and the back slash (\). Here is a PHP script example of single-quoted strings:

<?php 

echo 'Hello world!'; 

echo 'It\'s Friday!'; 

echo '\\ represents an operator.'; 

?>

This script will print:

Hello world!It's Friday!\ represents an operator.

Can You Specify the "new line" Character in Single-Quoted Strings?

You can not specify the "new line" character in a single-quoted string. If you don't believe, try this script:

<?php 

echo '\n will not work in single quoted strings.'; 

?>

This script will print:

\n will not work in single quoted strings.

How Many Escape Sequences Are Recognized in Single-Quoted Strings?

There are 2 escape sequences you can use in single-quoted strings:

• \\ - Represents the back slash character.
• \' - Represents the single quote character.

What Are the Special Characters You Need to Escape in Double-Quoted Stings?

There are two special characters you need to escape in a double-quote string: the double quote (") and the back slash (\). Here is a PHP script example of double-quoted strings:

<?php 

echo "Hello world!"; 

echo "Tom said: \"Who's there?\""; 

echo "\\ represents an operator."; 

?>

This script will print:

Hello world!Tom said: "Who's there?"\ represents an operator.

How Many Escape Sequences Are Recognized in Double-Quoted Strings?

There are 12 escape sequences you can use in double-quoted strings:

• \\ - Represents the back slash character.
• \" - Represents the double quote character.
• \$ - Represents the dollar sign.
• \n - Represents the new line character (ASCII code 10).
• \r - Represents the carriage return character (ASCII code 13).
• \t - Represents the tab character (ASCII code 9).
• \{ - Represents the open brace character.
• \} - Represents the close brace character.
• \[ - Represents the open bracket character.
• \] - Represents the close bracket character.
• \nnn - Represents a character as an octal value.
• \xnn - Represents a character as a hex value.

How To Include Variables in Double-Quoted Strings?

Variables included in double-quoted strings will be interpolated. Their values will be concatenated into the enclosing strings. For example, two statements in the following PHP script will print out the same string:

<?php 

$variable = "and";

echo "part 1 $variable part 2\n"; 

echo "part 1 ".$variable." part 2\n"; 

?>

This script will print:

part 1 and part 2

part 1 and part 2

How Many Ways to Include Variables in Double-Quoted Strings?

There are 3 formats to include variables in double-quoted strings:

• "part 1 $variable part 2" - This is the simplest format to include a variable in a string. The variable name starts with the dollar sign and ends at the first character that can not be used in variable name. Space is good character to end a variable name.
• "part 1${variable}part 2" - This format helps you to clearly end the variable name. The variable name starts at dollar sign before the open brace (${) and ends at the close brace (}).
• "part 1{$variable}part 2" - This format is also called complex format. You use this format to specify any complex variable expression in the same way as in a normal statement. The variable expression starts at ({$) followed by a variable name and ends at (}).

Here is a PHP script example of different ways to include variables in double-quoted strings:

<?php 

$beer = 'Heineken';

echo "$beer's taste is great.\n";

echo "He drank some ${beer}s and water.\n"; 

echo "She drank some {$beer}s and water.\n"; 

?>

This script will print:

Heineken's taste is great.

He drank some Heinekens and water.

She drank some Heinekens and water.

How Many Ways to Include Array Elements in Double-Quoted Strings?

There are 2 formats to include array elements in double-quoted strings:

• "part 1 $array[key] part 2" - This is called simple format. In this format, you can not specify the element key in quotes.
• "part 1 {$array['key']} part 2" - This is called complex format. In this format, the array element expression is specified in the same way as in a normal statement.

Here is a PHP script example of different ways to include variables in double-quoted strings:

<?php 

$fruits = array('strawberry' => 'red', 'banana' => 'yellow');

echo "A banana is $fruits[banana].\n";

echo "A banana is {$fruits['banana']}.\n";

?>

This script will print:

A banana is yellow.

A banana is yellow.

"A banana is $fruits['banana'].\n" will give you a syntax error.

How To Access a Specific Character in a String?

Any character in a string can be accessed by a special string element expression:

• $string{index} - The index is the position of the character counted from left and starting from 0.

Here is a PHP script example:

<?php 

$string = 'It\'s Friday!';

echo "The first character is $string{0}\n"; 

echo "The first character is {$string{0}}\n"; 

?>

This script will print:

The first character is It's Friday!{0}

The first character is I

How To Assigning a New Character in a String?

The string element expression, $string{index}, can also be used at the left side of an assignment statement. This allows you to assign a new character to any position in a string. Here is a PHP script example:

<?php 

$string = 'It\'s Friday?';

echo "$string\n";

$string{11} = '!';

echo "$string\n";

?>

This script will print:

It's Friday?

It's Friday!

How to Concatenate Two Strings Together?

You can use the string concatenation operator (.) to join two strings into one. Here is a PHP script example of string concatenation:

<?php 

echo 'Hello ' . "world!\n";

?>

This script will print:

Hello world!

How To Compare Two Strings with Comparison Operators?

PHP supports 3 string comparison operators, <, ==, and >, that generates Boolean values. Those operators use ASCII values of characters from both strings to determine the comparison results. Here is a PHP script on how to use comparison operators:

<?php

$a = "PHP is a scripting language.";

$b = "PHP is a general-purpose language.";

if ($a > $b) {

  print('$a > $b is true.'."\n");

} else {

  print('$a > $b is false.'."\n");

}

if ($a == $b) {

  print('$a == $b is true.'."\n");

} else {

  print('$a == $b is false.'."\n");

}

if ($a < $b) {

  print('$a < $b is true.'."\n");

} else {

  print('$a < $b is false.'."\n");

}

?>

This script will print:

$a > $b is true.

$a == $b is false.

$a < $b is false.

How To Convert Numbers to Strings?

In a string context, PHP will automatically convert any numeric value to a string. Here is a PHP script examples:

<?php 

print(-1.3e3);

print("\n");

print(strlen(-1.3e3));

print("\n");

print("Price = $" . 99.99 . "\n");

print(1 . " + " . 2 . " = " . 1+2 . "\n");

print(1 . " + " . 2 . " = " . (1+2) . "\n");

print(1 . " + " . 2 . " = 3\n");

print("\n");

?>

This script will print:

-1300

5

Price = $99.99

3

1 + 2 = 3

1 + 2 = 3

The print() function requires a string, so numeric value -1.3e3 is automatically converted to a string "-1300". The concatenation operator (.) also requires a string, so numeric value 99.99 is automatically converted to a string "99.99". Expression (1 . " + " . 2 . " = " . 1+2 . "\n") is a little bit interesting. The result is "3\n" because concatenation operations and addition operation are carried out from left to right. So when the addition operation is reached, we have "1 + 2 = 1"+2, which will cause the string to be converted to a value 1.

How To Convert Strings to Numbers?

In a numeric context, PHP will automatically convert any string to a numeric value. Strings will be converted into two types of numeric values, double floating number and integer, based on the following rules:

• The value is given by the initial portion of the string. If the string starts with valid numeric data, this will be the value used. Otherwise, the value will be 0 (zero).
• If the valid numeric data contains '.', 'e', or 'E', it will be converted to a double floating number. Otherwise, it will be converted to an integer.

Here is a PHP script example of converting some examples:

<?php 

$foo = 1 + "10.5";

echo "\$foo=$foo; type is " . gettype ($foo) . "\n";

$foo = 1 + "-1.3e3";

echo "\$foo=$foo; type is " . gettype ($foo) . "\n";

$foo = 1 + "bob-1.3e3";

echo "\$foo=$foo; type is " . gettype ($foo) . "\n";

$foo = 1 + "bob3";

echo "\$foo=$foo; type is " . gettype ($foo) . "\n";

$foo = 1 + "10 Small Pigs";

echo "\$foo=$foo; type is " . gettype ($foo) . "\n";

$foo = 4 + "10.2 Little Piggies";

echo "\$foo=$foo; type is " . gettype ($foo) . "\n";

$foo = "10.0 pigs " + 1;

echo "\$foo=$foo; type is " . gettype ($foo) . "\n";

$foo = "10.0 pigs " + 1.0;

echo "\$foo=$foo; type is " . gettype ($foo) . "\n";

?>

This script will print:

$foo=11.5; type is double

$foo=-1299; type is double

$foo=1; type is integer

$foo=1; type is integer

$foo=11; type is integer

$foo=14.2; type is double

$foo=11; type is double

$foo=11; type is double

How To Get the Number of Characters in a String?

You can use the "strlen()" function to get the number of characters in a string. Here is a PHP script example of strlen():

<?php 

print(strlen('It\'s Friday!'));

?>

This script will print:

12

How To Remove White Spaces from the Beginning and/or the End of a String?

There are 4 PHP functions you can use remove white space characters from the beginning and/or the end of a string:

• trim() - Remove white space characters from the beginning and the end of a string.
• ltrim() - Remove white space characters from the beginning of a string.
• rtrim() - Remove white space characters from the end of a string.
• chop() - Same as rtrim().

White space characters are defined as:

• " " (ASCII 32 (0x20)), an ordinary space.
• "\t" (ASCII 9 (0x09)), a tab.
• "\n" (ASCII 10 (0x0A)), a new line (line feed).
• "\r" (ASCII 13 (0x0D)), a carriage return.
• "\0" (ASCII 0 (0x00)), the NULL-byte.
• "\x0B" (ASCII 11 (0x0B)), a vertical tab.

Here is a PHP script example of trimming strings:

<?php

$text = "\t \t Hello world!\t \t ";

$leftTrimmed = ltrim($text);

$rightTrimmed = rtrim($text);

$bothTrimmed = trim($text);

print("leftTrimmed = ($leftTrimmed)\n");

print("rightTrimmed = ($rightTrimmed)\n");

print("bothTrimmed = ($bothTrimmed)\n");

?> 

This script will print:

leftTrimmed = (Hello world!              )

rightTrimmed = (                 Hello world!)

bothTrimmed = (Hello world!)

How To Remove the New Line Character from the End of a Text Line?

If you are using fgets() to read a line from a text file, you may want to use the chop() function to remove the new line character from the end of the line as shown in this PHP script:

<?php

$handle = fopen("/tmp/inputfile.txt", "r");

while ($line=fgets()) {

  $line = chop($line);

  # process $line here...

}

fclose($handle);

?> 

How To Remove Leading and Trailing Spaces from User Input Values?

If you are taking input values from users with a Web form, users may enter extra spaces at the beginning and/or the end of the input values. You should always use the trim() function to remove those extra spaces as shown in this PHP script:

<?php

$name = $_REQUEST("name");

$name = trim($name);

# $name is ready to be used...

?> 

How to Find a Substring from a Given String?

To find a substring in a given string, you can use the strpos() function. If you call strpos($haystack, $needle), it will try to find the position of the first occurrence of the $needle string in the $haystack string. If found, it will return a non-negative integer represents the position of $needle. Othewise, it will return a Boolean false. Here is a PHP script example of strpos():

<?php

$haystack1 = "2349534134345pickzycenter16504381640386488129";

$haystack2 = "pickzycenter234953413434516504381640386488129";

$haystack3 = "center234953413434516504381640386488129pickzy";

$pos1 = strpos($haystack1, "pickzycenter");

$pos2 = strpos($haystack2, "pickzycenter");

$pos3 = strpos($haystack3, "pickzycenter");

print("pos1 = ($pos1); type is " . gettype($pos1) . "\n");

print("pos2 = ($pos2); type is " . gettype($pos2) . "\n");

print("pos3 = ($pos3); type is " . gettype($pos3) . "\n");

?>

This script will print:

pos1 = (13); type is integer

pos2 = (0); type is integer

pos3 = (); type is boolean

"pos3" shows strpos() can return a Boolean value.

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