PHP Conditional Statements

This video was created by Dani Krossing

Conditional statements control the flow of a program by executing code only when certain conditions are met. Therefore, they are a fundamental part of a program's control flow.

The control flow is the order in which a computer executes statements in a script. When code is run, each statement is executed from top to bottom, unless there statements that alter the control flow, like conditionals statements or loops.

PHP has two main conditional statements, the if statement and the switch statement.

if

The most common and most used conditional statement is the if statement. The if statement determines whether or not to execute a block of code, by evaluating an expression. If the expression evaluates to TRUE the block of code will execute, otherwise, it will not.

<?php 
  $a = 4;
  $b = 3;

  // check if a is greater than b
  if ($a > $b) {
    echo "a is greater than b"; // this will execute
  }

  // check if a is less than b
  if ($a < $b) {
    echo "a is less than b"; // this will not execute
  }
?>

else

The else statement extends the if to execute a statement when the expression of the if statement evalutates to false.

<?php 
  $a = 4;
  $b = 3;

  // check if a is less than b
  if ($a < $b) {
    echo "a is less than b"; 
  } else {
    echo "a is not less than b"; // this will execute
  }
?>

elseif

The elseif statement ig used in conjunction with an if statement to provide an alternative path if the if statement's condition evaluated to FALSE. The elseif statement is tied to a specified condition, similar to the if statement, and will only execute if the condition evaluates to true. There is no limit to the number of elseif statement, but the else statement must always be the last in the line.

NOTE

In an if / elseif / else structure, conditions are only evaluated if the previous condition was FALSE.

<?php 
  $a = 3;
  $b = 4;

  // comparing a to b
  if ($a > $b) {
    echo "a is larger than b"; 
  } elseif ($a < $b) {
    echo "a is smaller than b";
  } else {
    echo "a is equal to b"; 
  }
?>

switch

The switch statement is an alternative to an if statement. With the switch statement you take a single variable or expression and compare it against a list of possible values, checking if they are equal.

When a switch statement finds a case that matches, it will execute that case's statement and then "fallthrough" all the remaining cases until it reaches the end of the switch block OR it finds a break statement. This is why in almost all cases, it is important to add a break at the end of each case.

The default case is to match anything that wasn't matched by other cases. It is the equivalent of the else statement.

<?php
  $a = 3; 

  switch ($a) {
    case 0:
      echo "a equals 0 <br>";
      break;
    case 1:
      echo "a equals 1 <br>";
      break;
    case 2:
      echo "a equals 2 <br>";
      break;
    case 3:
      echo "a equals 3 <br>";
      break;
    default:
      echo "a is not 0, 1, 2, or 3 <br>";
      break;
  }
?>