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PHP for loop Exercises: Using nested for loop, construct a specific pattern

PHP for loop: Exercise-4 with Solution

Create a script to construct the following pattern, using a nested for loop.

* 
* * 
* * * 
* * * * 
* * * * * 
* * * * * 
* * * * 
* * * 
* * 
* 

Pictorial Presentation:

PHP for loop Exercises: Using nested for loop, construct a specific pattern

Sample Solution:

PHP Code:

<?php
$n=5;
for($i=1; $i<=$n; $i++)
{
for($j=1; $j<=$i; $j++)
{
echo ' * ';
}
echo '\n';
}
for($i=$n; $i>=1; $i--)
{
for($j=1; $j<=$i; $j++)
{
echo ' * ';
}
echo '\n ';
}
?>

Sample Output:

 *                                                          
 *  *                                                       
 *  *  *                                                    
 *  *  *  *                                                 
 *  *  *  *  *                                              
 *  *  *  *  *                                              
 *  *  *  *                                                 
 *  *  *                                                    
 *  *                                                       
 * 

Flowchart :

Flowchart: Using nested for loop, construct a specific pattern

PHP Code Editor:

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Previous: Create a script to construct the specific pattern, using nested for loop.
Next: Write a program to calculate and print the factorial of a number using a for loop. The factorial of a number is the product of all integers up to and including that number, so the factorial of 4 is 4*3*2*1= 24.

What is the difficulty level of this exercise?



PHP: Tips of the Day

PHP - How do I implement a callback in PHP?

The manual uses the terms "callback" and "callable" interchangeably, however, "callback" traditionally refers to a string or array value that acts like a function pointer, referencing a function or class method for future invocation. This has allowed some elements of functional programming since PHP 4. The flavors are:

$cb1 = 'someGlobalFunction';
$cb2 = ['ClassName', 'someStaticMethod'];
$cb3 = [$object, 'somePublicMethod'];

// this syntax is callable since PHP 5.2.3 but a string containing it
// cannot be called directly
$cb2 = 'ClassName::someStaticMethod';
$cb2(); // fatal error

// legacy syntax for PHP 4
$cb3 = array(&$object, 'somePublicMethod');

This is a safe way to use callable values in general:

if (is_callable($cb2)) {
    // Autoloading will be invoked to load the class "ClassName" if it's not
    // yet defined, and PHP will check that the class has a method
    // "someStaticMethod". Note that is_callable() will NOT verify that the
    // method can safely be executed in static context.

    $returnValue = call_user_func($cb2, $arg1, $arg2);
}

Modern PHP versions allow the first three formats above to be invoked directly as $cb(). call_user_func and call_user_func_array support all the above.

Notes/Caveats:

  1. If the function/class is namespaced, the string must contain the fully-qualified name. E.g. ['Vendor\Package\Foo', 'method']
  2. call_user_func does not support passing non-objects by reference, so you can either use call_user_func_array or, in later PHP versions, save the callback to a var and use the direct syntax: $cb();
  3. Objects with an __invoke() method (including anonymous functions) fall under the category "callable" and can be used the same way, but I personally don't associate these with the legacy "callback" term.
  4. The legacy create_function() creates a global function and returns its name. It's a wrapper for eval() and anonymous functions should be used instead.

Ref : https://bit.ly/2Zmqil0