PHP logical Interview Questions and Answers that every developer should be know.

Question 1: What will be the results of $a and why?

$a = 2; 
function foo() { 
 $a = 3;  
} 

foo(); 
echo $a;

Answer: The output of the above code will be "2" because here we are calling the function foo() but $a=3 scope will be only inside the function.

Question 2: What is the cause of this warning: 'Warning: Cannot modify header information - headers already sent', and what is a good practice to prevent it?
Answer: Cause: body data was sent, causing headers to be sent too.
Prevention: Be sure to execute header specific code first before you output any body data. Be sure you haven't accidentally sent out whitespace or any other characters.

Question 3: What is wrong with this query: "SELECT * FROM table WHERE id = $_POST[ 'id' ]"?
Answer:

1. It is vulnarable to SQL injection. Never use user input directly in queries. Sanitize it first. Preferebly use prepared statements (PDO).
2. Don't select all columns (*), but specify every single column. This is predominantly ment to prevent queries hogging up memory when for instance a BLOB column is added at some point in the future

Question 4: What is wrong with this if statement: if( !strpos( $haystack, $needle )?
Answer: strpos returns the index position of where it first found the $needle, which could be 0. Since 0 also resolves to false the solution is to use strict comparison: if( false !== strpos( $haystack, $needle ).

Question 5: What is the preferred way to write this if statement, and why?
if( 5 == $someVar ) or if( $someVar == 5 )
Answer: The former, as it prevents accidental assignment of 5 to $someVar when you forget to use 2 equalsigns ($someVar = 5), and will cause an error, the latter won't.

Question 6: Given this code:

function doSomething( &$arg )
{
    $return = $arg;
    $arg += 1;
    return $return;
}

$a = 3;
$b = doSomething( $a );

what is the value of $a and $b after the function call and why?
Answer: $a is 4 and $b is 3. The former because $arg is passed by reference, and the latter because the return value of the function is a copy of (not a reference to) the initial value of the argument.

Question 7: What is the difference between public, protected and private in a class definition?
Answer: public makes a class member available to "everyone", protected makes the class member available to only itself and derived classes, private makes the class member only available to the class itself.

Question 8: What is wrong with this code:

class SomeClass
{
    protected $_someMember;

    public function __construct()
    {
        $this->_someMember = 1;
    }

    public static function getSomethingStatic()
    {
        return $this->_someMember * 5; // here's the catch
    }
}

Answer: Static methods don't have access to $this, because static methods can be executed without instantiating a class.

Question 9: What is the difference between an interface and an abstract class?
Answer: An interface defines a contract between an implementing class is and an object that calls the interface. An abstract class pre-defines certain behavior for classes that will extend it. To a certain degree this can also be considered a contract, since it garantuees certain methods to exist.

Question 10: What is wrong with classes that predominantly define getters and setters, that map straight to it's internal members, without actually having methods that execute behaviour?
Answer: This might be a code smell since the object acts as an ennobled array, without much other use.

Question 11: What will be the results of $a and why?

$a = 2; 
function foo() { 
 $a += 3; 
 return $a; 
} 

$a = foo(); 
echo $a;

Answer: It's showing Notice: Undefined variable: a. Because in the first line of function, we are doing $a = $a +3 but here $a is not defined into the function it's defined outside of the function "foo".

Question 12: What would be the output of the following:

$a = '1';
echo $b = &$a;
echo $c = "2$b";

Answer:  

1.  1     // $b value will be 1
2.  21  // $c value will be 21 as 2 is concatenated to the value of $b.

Question 13: What would be the output of the following?

var_dump(0123 == 123);
var_dump('0123' == 123);
var_dump('0123' === 123);

 Answer: 

1. bool(false)   //  As a number preceded by 0 leads to an octal number.
2. bool(true)    // as 0123 is enclosed in quotes so it would be converted to its numeric value which is 123 so it is true.
3. bool(false)  // it's false as o123 is quoted and is a string so they are not identical. Their data type is different. 

Question 14: What will be the output of the following:
Answer:  bool(true)   //  and operator works as OR because the = operator has precedence over and.

Question 15: What would be the output of the following:

$array = array(
1 => "a",
"1" => "b",
1.5 => "c",
true => "d",
);

Answer:  Array ( [1] => d ) Explain: Here all keys will be typecast to number 1. But the value the array will hold will be of the data type whose precedence is higher precedence hierarchy in increment order is as follows: String("1")  => Number(1) => Float(1.5) => bool(true).  

So if we omit a true element from the array then the result will be Array ( [1] => c )  and so like that.

Question 16: Write a Program for Bubble sorting in ascending order?
Answer: Click Here to See the Answer

Question 17: How to calculate the number of weeks between two dates using javascript?
Answer: Click Here to See the Answer

Question 18: How to calculate the number of months between two dates using javascript?
 Answer: Click Here to See the Answer

Question 19: What is the difference between a HAVING CLAUSE and a WHERE CLAUSE?
Answer: Click Here to See the Answer

Question 20: How to swap two numbers without using a third variable?
 Answer: Click Here to See the Answer

Question 21: Write a program to find the biggest number in an array without using any array functions using PHP?
Answer: Click Here to See the Answer

Question 22: Write a program to print the Fibonacci series using PHP? 
Answer: Click Here to See the Answer

Question 23: Remove duplicate elements from an array without using a built-in function using PHP? 
Answer: Click Here to See the Answer

Question 24: How to Delete records from the different tables without using a subquery using MySQL?
Answer: Click Here to See the Answer

Question 25: How to Delete the first or last index and value of an array using PHP?
Answer: Click Here to See the Answer

Question 26: How to Get the Second, Third, Fourth, or nth Largest Salary using Mysql or Sql? 
Answer: Click Here to See the Answer

 

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Best Of Luck For Your Interview.