For loop to While loop Java

<?php

    int[] numbers = {10, 20, 30, 40, 50};

    int i = 0;

    while (i < numbers.length) {

        int currentValue = numbers[i];

        if (currentValue == 30) {

            break;

        }

        System.out.println(currentValue);

        i++;

    }

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For loop to While loop Java

<?php

    int[] numbers = {10, 20, 30, 40, 50};

    int i = 0;

    while (i < numbers.length) {

        int currentValue = numbers[i];

        if (currentValue == 30) {

            break;

        }

        System.out.println(currentValue);

        i++;

    }

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How to find duplicate elements in array in effective way. I mean to say with very less iterations

<?php

    Using Characters here, as give more flexibility.

    Character[] arrayC= (new Character[] { 'a', 'a', 'a', 'b', 'b' ,'v'});

    List<Character> allChars= new ArrayList<>(Arrays.asList(arrayC));

    List<Character> duplicates = allChars.stream().distinct().filter(

                                entry -> Collections.frequency(allChars, entry) > 1).

                                collect(Collectors.toList());

    // duplicates  --> 'a','b'

    First the array is converted into an ArrayList. Then, if finds some entry that is repeated more than once, it collects it into duplicates.

    If you want to get which are not duplicates, just:

    allChars.removeAll(duplicates);

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How to find duplicate elements in array in effective way. I mean to say with very less iterations

<?php

    Using Characters here, as give more flexibility.

    Character[] arrayC= (new Character[] { 'a', 'a', 'a', 'b', 'b' ,'v'});

    List<Character> allChars= new ArrayList<>(Arrays.asList(arrayC));

    List<Character> duplicates = allChars.stream().distinct().filter(

                                entry -> Collections.frequency(allChars, entry) > 1).

                                collect(Collectors.toList());

    // duplicates  --> 'a','b'

    First the array is converted into an ArrayList. Then, if finds some entry that is repeated more than once, it collects it into duplicates.

    If you want to get which are not duplicates, just:

    allChars.removeAll(duplicates);

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How can I create every combination possible for the contents of two arrays?

<?php

    A loop of this form

    combos = [] //or combos = new Array(2);

    for(var i = 0; i < array1.length; i++)

    {

        for(var j = 0; j < array2.length; j++)

        {

            //you would access the element of the array as array1[i] and array2[j]

            //create and array with as many elements as the number of arrays you are to combine

            //add them in

            //you could have as many dimensions as you need

            combos.push(array1[i] + array2[j])

        }

    }

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How can I create every combination possible for the contents of two arrays?

<?php

    A loop of this form

    combos = [] //or combos = new Array(2);

    for(var i = 0; i < array1.length; i++)

    {

        for(var j = 0; j < array2.length; j++)

        {

            //you would access the element of the array as array1[i] and array2[j]

            //create and array with as many elements as the number of arrays you are to combine

            //add them in

            //you could have as many dimensions as you need

            combos.push(array1[i] + array2[j])

        }

    }

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How to remove empty lines space in Visual Studio Code

 How to remove empty lines in Visual Studio Code

Method 1:

Here are step by step instructions to remove those empty lines.

1. Open your code in Visual Studio Code
2. From Edit Menu, select Replace or use a short cut key (command + Option + F on Mac or Ctrl + H on Windows)
3. In the find box type \n\n
4. In the replace box type \n
5. Make sure the 'Use Regular Expression' is selected
6. Select 'Replace All' button
    

Method 2:

The above method should remove all the empty line however, if it didn’t then follow these steps:

1. Open your code in Visual Studio Code
2. From Edit Menu, select Replace or use a short cut key (command + Option + F on Mac or Ctrl + H on Windows)
3. In the find box type ^(\s)*$\n
4. Leave the replace box empty
5. Make sure the 'Use Regular Expression' is selected
6. Select 'Replace All' button 

If you can't find the above steps, here is a picture.

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How to remove empty lines space in Visual Studio Code

 How to remove empty lines in Visual Studio Code

Method 1:

Here are step by step instructions to remove those empty lines.

1. Open your code in Visual Studio Code
2. From Edit Menu, select Replace or use a short cut key (command + Option + F on Mac or Ctrl + H on Windows)
3. In the find box type \n\n
4. In the replace box type \n
5. Make sure the 'Use Regular Expression' is selected
6. Select 'Replace All' button
    

Method 2:

The above method should remove all the empty line however, if it didn’t then follow these steps:

1. Open your code in Visual Studio Code
2. From Edit Menu, select Replace or use a short cut key (command + Option + F on Mac or Ctrl + H on Windows)
3. In the find box type ^(\s)*$\n
4. Leave the replace box empty
5. Make sure the 'Use Regular Expression' is selected
6. Select 'Replace All' button 

If you can't find the above steps, here is a picture.

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Reference — What does this symbol mean in PHP?

 

    Incrementing / Decrementing Operators

    ++ increment operator

    -- decrement operator

    Example    Name              Effect

    ---------------------------------------------------------------------

    ++$a       Pre-increment     Increments $a by one, then returns $a.

    $a++       Post-increment    Returns $a, then increments $a by one.

    --$a       Pre-decrement     Decrements $a by one, then returns $a.

    $a--       Post-decrement    Returns $a, then decrements $a by one.

    These can go before or after the variable.

    If put before the variable, the increment/decrement operation is done to the variable first then the result is returned. If put after the variable, the variable is first returned, then the increment/decrement operation is done.

    For example:

    $apples = 10;

    for ($i = 0; $i < 10; ++$i) {

        echo 'I have ' . $apples-- . " apples. I just ate one.\n";

    }

    Live example

    In the case above ++$i is used, since it is faster. $i++ would have the

     same results.

    Pre-increment is a little bit faster because it really increments the 

    variable and after that 'returns' the result. Post-increment creates 

    a special variable, copies there the value of the first variable and

     only after the first variable is used, replaces its value with second's.

    However, you must use $apples--, since first, you want to display the 

    current number of apples, and then you want to subtract one from it.

    You can also increment letters in PHP:

    $i = "a";

    while ($i < "c") {

        echo $i++;

    }

    Once z is reached aa is next, and so on.

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Reference — What does this symbol mean in PHP?

 

    Incrementing / Decrementing Operators

    ++ increment operator

    -- decrement operator

    Example    Name              Effect

    ---------------------------------------------------------------------

    ++$a       Pre-increment     Increments $a by one, then returns $a.

    $a++       Post-increment    Returns $a, then increments $a by one.

    --$a       Pre-decrement     Decrements $a by one, then returns $a.

    $a--       Post-decrement    Returns $a, then decrements $a by one.

    These can go before or after the variable.

    If put before the variable, the increment/decrement operation is done to the variable first then the result is returned. If put after the variable, the variable is first returned, then the increment/decrement operation is done.

    For example:

    $apples = 10;

    for ($i = 0; $i < 10; ++$i) {

        echo 'I have ' . $apples-- . " apples. I just ate one.\n";

    }

    Live example

    In the case above ++$i is used, since it is faster. $i++ would have the

     same results.

    Pre-increment is a little bit faster because it really increments the 

    variable and after that 'returns' the result. Post-increment creates 

    a special variable, copies there the value of the first variable and

     only after the first variable is used, replaces its value with second's.

    However, you must use $apples--, since first, you want to display the 

    current number of apples, and then you want to subtract one from it.

    You can also increment letters in PHP:

    $i = "a";

    while ($i < "c") {

        echo $i++;

    }

    Once z is reached aa is next, and so on.

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How do you parse and process HTML/XML in PHP?

    <?php

    How do you parse and process HTML/XML in PHP?

    Examples:

    

    How to get HTML elements:

    // Create DOM from URL or file

    $html = file_get_html('http://www.example.com/');

    

    // Find all images

    foreach($html->find('img') as $element)

            echo $element->src . '<br>';

    

    // Find all links

    foreach($html->find('a') as $element)

            echo $element->href . '<br>';

    

    

    How to modify HTML elements:

    // Create DOM from string

    $html = str_get_html('<div id="hello">Hello</div><div id="world">World</div>');

    

    $html->find('div', 1)->class = 'bar';

    

    $html->find('div[id=hello]', 0)->innertext = 'foo';

    

    echo $html;

    

    

    Extract content from HTML:

    // Dump contents (without tags) from HTML

    echo file_get_html('http://www.google.com/')->plaintext;

    

    

    Scraping Slashdot:

    // Create DOM from URL

    $html = file_get_html('http://slashdot.org/');

    

    // Find all article blocks

    foreach($html->find('div.article') as $article) {

        $item['title']     = $article->find('div.title', 0)->plaintext;

        $item['intro']    = $article->find('div.intro', 0)->plaintext;

        $item['details'] = $article->find('div.details', 0)->plaintext;

        $articles[] = $item;

    }

    

    print_r($articles);

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How do you parse and process HTML/XML in PHP?

    <?php

    How do you parse and process HTML/XML in PHP?

    Examples:

    

    How to get HTML elements:

    // Create DOM from URL or file

    $html = file_get_html('http://www.example.com/');

    

    // Find all images

    foreach($html->find('img') as $element)

            echo $element->src . '<br>';

    

    // Find all links

    foreach($html->find('a') as $element)

            echo $element->href . '<br>';

    

    

    How to modify HTML elements:

    // Create DOM from string

    $html = str_get_html('<div id="hello">Hello</div><div id="world">World</div>');

    

    $html->find('div', 1)->class = 'bar';

    

    $html->find('div[id=hello]', 0)->innertext = 'foo';

    

    echo $html;

    

    

    Extract content from HTML:

    // Dump contents (without tags) from HTML

    echo file_get_html('http://www.google.com/')->plaintext;

    

    

    Scraping Slashdot:

    // Create DOM from URL

    $html = file_get_html('http://slashdot.org/');

    

    // Find all article blocks

    foreach($html->find('div.article') as $article) {

        $item['title']     = $article->find('div.title', 0)->plaintext;

        $item['intro']    = $article->find('div.intro', 0)->plaintext;

        $item['details'] = $article->find('div.details', 0)->plaintext;

        $articles[] = $item;

    }

    

    print_r($articles);

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StartsWith() and endsWith() functions in PHP

    <?php

    startsWith() and endsWith() functions in PHP

    function startsWith( $haystack, $needle ) {

        $length = strlen( $needle );

        return substr( $haystack, 0, $length ) === $needle;

    }

    function endsWith( $haystack, $needle ) {

    $length = strlen( $needle );

    if( !$length ) {

        return true;

    }

    return substr( $haystack, -$length ) === $needle;

    }

    Use this if you don't want to use a regex.

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StartsWith() and endsWith() functions in PHP

    <?php

    startsWith() and endsWith() functions in PHP

    function startsWith( $haystack, $needle ) {

        $length = strlen( $needle );

        return substr( $haystack, 0, $length ) === $needle;

    }

    function endsWith( $haystack, $needle ) {

    $length = strlen( $needle );

    if( !$length ) {

        return true;

    }

    return substr( $haystack, -$length ) === $needle;

    }

    Use this if you don't want to use a regex.

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Deleting an element from an array in PHP

 <?php

There are different ways to delete an array element, where some are more useful for some specific tasks than others.

Deleting a single array element

If you want to delete just one array element you can use unset() or alternatively \array_splice().

If you know the value and don’t know the key to delete the element you can use \array_search() to get the key. This only works if the element does not occur more than once, since \array_search returns the first hit only.

unset()

Note that when you use unset() the array keys won’t change. If you want to reindex the keys you can use \array_values() after unset(), which will convert all keys to numerically enumerated keys starting from 0.

Code:

$array = [0 => "a", 1 => "b", 2 => "c"];

unset($array[1]);

          // ↑ Key which you want to delete

Output:

[

    [0] => a

    [2] => c

]

\array_splice() method

If you use \array_splice() the keys will automatically be reindexed, but the associative keys won’t change — as opposed to \array_values(), which will convert all keys to numerical keys.

\array_splice() needs the offset, not the key, as the second parameter.

Code:

$array = [0 => "a", 1 => "b", 2 => "c"];

\array_splice($array, 1, 1);

                   // ↑ Offset which you want to delete

Output:

[

    [0] => a

    [1] => c

]

array_splice(), same as unset(), take the array by reference. You don’t assign the return values of those functions back to the array.

Deleting multiple array elements

If you want to delete multiple array elements and don’t want to call unset() or \array_splice() multiple times you can use the functions \array_diff() or \array_diff_key() depending on whether you know the values or the keys of the elements which you want to delete.

\array_diff() method

If you know the values of the array elements which you want to delete, then you can use \array_diff(). As before with unset() it won’t change the keys of the array.

Code:

$array = [0 => "a", 1 => "b", 2 => "c", 3 => "c"];

$array = \array_diff($array, ["a", "c"]);

                          // └────────┘

                          // Array values which you want to delete

Output:

[

    [1] => b

]

\array_diff_key() method

If you know the keys of the elements which you want to delete, then you want to use \array_diff_key(). You have to make sure you pass the keys as keys in the second parameter and not as values. Keys won’t reindex.

Code:

$array = [0 => "a", 1 => "b", 2 => "c"];

$array = \array_diff_key($array, [0 => "xy", "2" => "xy"]);

                               // ↑           ↑

                               // Array keys which you want to delete

Output:

[

    [1] => b

]

If you want to use unset() or \array_splice() to delete multiple elements with the same value you can use \array_keys() to get all the keys for a specific value and then delete all elements.

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Deleting an element from an array in PHP

 <?php

There are different ways to delete an array element, where some are more useful for some specific tasks than others.

Deleting a single array element

If you want to delete just one array element you can use unset() or alternatively \array_splice().

If you know the value and don’t know the key to delete the element you can use \array_search() to get the key. This only works if the element does not occur more than once, since \array_search returns the first hit only.

unset()

Note that when you use unset() the array keys won’t change. If you want to reindex the keys you can use \array_values() after unset(), which will convert all keys to numerically enumerated keys starting from 0.

Code:

$array = [0 => "a", 1 => "b", 2 => "c"];

unset($array[1]);

          // ↑ Key which you want to delete

Output:

[

    [0] => a

    [2] => c

]

\array_splice() method

If you use \array_splice() the keys will automatically be reindexed, but the associative keys won’t change — as opposed to \array_values(), which will convert all keys to numerical keys.

\array_splice() needs the offset, not the key, as the second parameter.

Code:

$array = [0 => "a", 1 => "b", 2 => "c"];

\array_splice($array, 1, 1);

                   // ↑ Offset which you want to delete

Output:

[

    [0] => a

    [1] => c

]

array_splice(), same as unset(), take the array by reference. You don’t assign the return values of those functions back to the array.

Deleting multiple array elements

If you want to delete multiple array elements and don’t want to call unset() or \array_splice() multiple times you can use the functions \array_diff() or \array_diff_key() depending on whether you know the values or the keys of the elements which you want to delete.

\array_diff() method

If you know the values of the array elements which you want to delete, then you can use \array_diff(). As before with unset() it won’t change the keys of the array.

Code:

$array = [0 => "a", 1 => "b", 2 => "c", 3 => "c"];

$array = \array_diff($array, ["a", "c"]);

                          // └────────┘

                          // Array values which you want to delete

Output:

[

    [1] => b

]

\array_diff_key() method

If you know the keys of the elements which you want to delete, then you want to use \array_diff_key(). You have to make sure you pass the keys as keys in the second parameter and not as values. Keys won’t reindex.

Code:

$array = [0 => "a", 1 => "b", 2 => "c"];

$array = \array_diff_key($array, [0 => "xy", "2" => "xy"]);

                               // ↑           ↑

                               // Array keys which you want to delete

Output:

[

    [1] => b

]

If you want to use unset() or \array_splice() to delete multiple elements with the same value you can use \array_keys() to get all the keys for a specific value and then delete all elements.

Read More

How can I prevent SQL injection in PHP?

 <?php 

Use prepared statements and parameterized queries. These are SQL statements that are sent to and parsed by the database server separately from any parameters. This way it is impossible for an attacker to inject malicious SQL.
You basically have two options to achieve this


Using PDO (for any supported database driver):
    $stmt = $pdo->prepare('SELECT * FROM employees WHERE name = :name');
    
    $stmt->execute([ 'name' => $name ]);
    
    foreach ($stmt as $row) {
        // Do something with $row
    }
    Using MySQLi (for MySQL):
    
    $stmt = $dbConnection->prepare('SELECT * FROM employees WHERE name = ?');
    $stmt->bind_param('s', $name); // 's' specifies the variable type => 'string'
    
    $stmt->execute();
    
    $result = $stmt->get_result();
    while ($row = $result->fetch_assoc()) {
        // Do something with $row
    }
    If you're connecting to a database other than MySQL, there is a driver-specific second option that you can refer to (for example, pg_prepare() and pg_execute() for PostgreSQL). PDO is the universal option.
    
    Correctly setting up the connection
    Note that when using PDO to access a MySQL database real prepared statements are not used by default. To fix this you have to disable the emulation of prepared statements. An example of creating a connection using PDO is:


    $dbConnection = new PDO('mysql:dbname=dbtest;host=127.0.0.1;charset=utf8', 'user', 'password');
    $dbConnection->setAttribute(PDO::ATTR_EMULATE_PREPARES, false);
    $dbConnection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    In the above example the error mode isn't strictly necessary, but it is advised to add it. This way the script will not stop with a Fatal Error when something goes wrong. And it gives the developer the chance to catch any error(s) which are thrown as PDOExceptions.
    What is mandatory, however, is the first setAttribute() line, which tells PDO to disable emulated prepared statements and use real prepared statements. This makes sure the statement and the values aren't parsed by PHP before sending it to the MySQL server (giving a possible attacker no chance to inject malicious SQL).
    Although you can set the charset in the options of the constructor, it's important to note that 'older' versions of PHP (before 5.3.6) silently ignored the charset parameter in the DSN.
   **- Explanation -**
    The SQL statement you pass to prepare is parsed and compiled by the database server. By specifying parameters (either a ? or a named parameter like :name in the example above) you tell the database engine where you want to filter on. Then when you call execute, the prepared statement is combined with the parameter values you specify.
    The important thing here is that the parameter values are combined with the compiled statement, not an SQL string. SQL injection works by tricking the script into including malicious strings when it creates SQL to send to the database. So by sending the actual SQL separately from the parameters, you limit the risk of ending up with something you didn't intend.
    Any parameters you send when using a prepared statement will just be treated as strings (although the database engine may do some optimization so parameters may end up as numbers too, of course). In the example above, if the $name variable contains 'Sarah'; DELETE FROM employees the result would simply be a search for the string "'Sarah'; DELETE FROM employees", and you will not end up with an empty table.
    Another benefit of using prepared statements is that if you execute the same statement many times in the same session it will only be parsed and compiled once, giving you some speed gains.
    Oh, and since you asked about how to do it for an insert, here's an example (using PDO):
    $preparedStatement = $db->prepare('INSERT INTO table (column) VALUES (:column)');
    $preparedStatement->execute([ 'column' => $unsafeValue ]);
    
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