Using control structures and loops in PHP

Control structures and loops are an essential part of programming in general, as they allow you to control the flow of your program and perform operations on data. In PHP, there are several types of control structures and loops that you can use to manipulate data, which we are going to discuss in this article.

If Statements

If statements are used to execute a block of code only if a certain condition is met. Here is the basic syntax for an if statement:

<?php
  if (condition) {
    // code to be executed if condition is true
  }
?>

You can also add an else clause to execute a block of code if the condition in the above statement is not met:

<?php
  if (condition) {
    // code to be executed if condition is true
  } else {
    // code to be executed if condition is false
  }
?>

If there are additional conditions to check you can also use elseif clauses to add the additional conditions to be checked:

<?php
  if (condition1) {
    // code to be executed if condition1 is true
  } elseif (condition2) {
    // code to be executed if condition1 is false and condition2 is true
  } else {
    // code to be executed if condition1 and condition2 are false
  }
?>

Switch Statements

Switch statements are another way to execute a block of code based on a particular value. Here is the basic syntax for a switch statement:

<?php
    switch (expression) {
    case value1:
      // code to be executed if expression equals value1
      break;
    case value2:
      // code to be executed if expression equals value2
      break;
    default:
      // code to be executed if expression does not match any of the case values
  }
?>

The expression is evaluated, and the code block corresponding to the first case value that matches the expression is executed. If none of the case values match the expression, the code block in the default clause is executed.

READ ALSO: VARIABLES, CONSTANTS, AND EXPRESSIONS IN PHP

The break statements are used to exit the switch statement once a matching case has been found. If you omit the break statement, the code will continue to execute into the next case.

Here is an example of a switch statement that converts a string to uppercase:

<?php
    $string = "hello";
    
    switch ($string) {
      case "hello":
        $string = "HELLO";
        break;
      case "world":
        $string = "WORLD";
        break;
      default:
        $string = "UNKNOWN";
    }
    
    echo $string; // output: HELLO
?>

In this example, the expression is $string, which is evaluated as “hello”. The code block in the hello case is executed, and the value of $string is set to “HELLO”. The break statement causes the switch statement to exit, so the code in the world and default cases is not executed.

Switch statements are often used as an alternative to a series of if-else statements, especially when you have a large number of conditions to check. They can make your code more readable and easier to maintain.

It’s important to note that the expression in a switch statement can only be a scalar value (integer, float, string, or boolean). You cannot use an array or an object as the expression. If you need to perform complex comparisons or evaluations, you should use an if-else statement or a different control structure.

Loops

Loops allow you to repeat a block of code a certain number of times or until a certain condition is met. The following are the basic types of loop in PHP:

For Loops

A for loop in PHP is a control structure that allows you to execute a block of code a specific number of times. It has three parts: the initialization, the condition, and the iteration.

The initialization is executed before the loop begins, and it is used to initialize a counter variable. The condition is checked before each iteration of the loop, and if it is true, the loop will continue. The iteration is executed at the end of each iteration of the loop, and it is used to update the counter variable. Here is the basic syntax for a for loop in PHP:

<?php
  for (initialization; condition; iteration) {
    // code to be executed
  }

?>

Here is the basic syntax for a for loop that counts from 1 to 10:

<?php
  for ($i = 1; $i <= 10; $i++) {
    echo $i . "\n";
  }
?>

The loop above will output the numbers from 1 to 10, one per line.

The initialization sets the value of $i to 1. The condition is $i <= 10, which means the loop will continue as long as $i is less than or equal to 10. The iteration is $i++, which means that $i will be incremented by 1 at the end of each iteration.

For loops can also used to iterate over arrays.

<?php
  $names = array("John", "Abel", "Jessica");
  
  for ($i = 0; $i < count($names); $i++) {
    echo $names[$i] . "\n";
  }
?>

This will output the elements of the $names array, one per line.

It’s important to note that for loops should be used when you know the number of iterations in advance. If you don’t know the number of iterations, you should use a different type of loop, such as a while or do-while loop.

While Loops

A while loop in PHP is a control structure that allows you to execute a block of code as long as a certain condition is met. It has the following syntax:

<?php
  while (condition) {
    // code to be executed
  }
?>

The condition is checked before each iteration of the loop, and if it is true, the loop will continue. If the condition is false, the loop will exit.

Here is an example of a while loop that counts from 1 to 10:

<?php
  $i = 1;
  while ($i <= 10) {
    echo $i . "\n";
    $i++;
  }
?>

The loop above will output the numbers from 1 to 10, one per line.

The variable $i is initialized to 1 before the loop begins. The condition is $i <= 10, which means the loop will continue as long as $i is less than or equal to 10. The $i++ statement is executed at the end of each iteration, which means that $i is incremented by 1 each time through the loop.

While loops are often used when you don’t know the number of iterations in advance, or when you want to keep looping until a certain condition is met.

It’s important to be careful with while loops, as they can easily become infinite loops if the condition is always true. Make sure that the condition will eventually become false, or use a different type of loop, such as a for loop, if you know the number of iterations in advance.

Do-While Loops

A do-while loop in PHP is a control structure that allows you to execute a block of code at least once, and then repeat the block as long as a certain condition is met. It has the following syntax:

<?php
    do {
      // code to be executed
    } while (condition);
?>

The code block will be executed at least once, and then the condition will be checked. If the condition is true, the loop will continue. If the condition is false, the loop will exit.

Here is an example of a do-while loop that counts from 1 to 10:

<?php
  $i = 1;
  do {
    echo $i . "\n";
    $i++;
  } while ($i <= 10);
?>

The loop above will output the numbers from 1 to 10, one per line.

The variable $i is initialized to 1 before the loop begins. The $i++ statement is executed at the end of each iteration, which means that $i is incremented by 1 each time through the loop. The condition is $i <= 10, which means the loop will continue as long as $i is less than or equal to 10.

Do-while loops are similar to while loops, but they will always execute the code block at least once, even if the condition is false. This can be useful if you want to ensure that the code block is executed at least once, and then repeat it if necessary.

It’s important to be careful with do-while loops, as they can easily become infinite loops if the condition is always true. Make sure that the condition will eventually become false, or use a different type of loop if you know the number of iterations in advance.

Foreach Loops

A foreach loop in PHP is a control structure that allows you to iterate over the elements of an array. It has the following syntax:

<?php
  foreach (array as $value) {
    // code to be executed
  }
?>

OR

<?php
  foreach (array as $key => $value) {
    // code to be executed
  }
?>

The first form of the loop will iterate over the values of the array, and the second form will iterate over both the keys and values of the array.

Here is an example of a foreach loop that iterates over both the keys and values of an array:

<?php
  $names = array("John", "Ana", "Jessica");
  
  foreach ($names as $index => $name) {
    echo $index . ": " . $name . "\n";
  }
?>

This will output the keys and values of the $names array, in the format “key: value”, one per line.

Foreach loops are a concise and easy-to-read way to iterate over arrays in PHP. They are especially useful when you don’t need to know the index of the current element, and you just want to access the values of the array.

It’s important to note that foreach loops only work with arrays and objects that implement the Traversable interface. You cannot use a foreach loop to iterate over a simple variable or expression. If you need to iterate over a range of numbers, you can use a for loop or a range() function.