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Switch Statements

The switch statement in PHP is a type of control structure that allows you to execute different pieces of code based on the value of a single expression. The switch statement compares the value of the expression to the values of multiple cases and executes the code associated with the first case that matches.

Basic syntax

Here's the basic syntax for a switch statement in PHP:

switch (expression) {
  case value1:
    // code to be executed if expression = value1;
    break;
  case value2:
    // code to be executed if expression = value2;
    break;
  case value3:
    // code to be executed if expression = value3;
    break;
  default:
    // code to be executed if the expression doesn't match any of the values
    break;
}

The expression in a switch statement can be any expression that returns a value (integer, string, or float).

The case statements define the different values to be tested against the expression. Each case is followed by a colon (:) and a block of code that will be executed if the expression matches that case.

The break statement is used to break out of the switch statement once a matching case has been found and its code has been executed. If a break statement is not included at the end of a case, the code from that case will continue to execute until the end of the switch statement or the next break statement.

The default case is used to provide a fallback option in case the expression does not match any of the case values. If the default case is not provided and no matching case is found, the switch statement will simply exit without executing any code.

Using switch statements

Switch statements seem to be similar to if statements.

Using an if statement

For example, let's say we wanted to display the day of the week to the user. We can do this with a chain of if elseif statements like so:

This would output the following:

Today is Monday.

While this solution is viable, you may want to use a switch statement when trying to write cleaner code.

$day = "Monday";
 
if ($day === "Monday") {
  echo "Today is Monday.";
} elseif ($day === "Tuesday") {
  echo "Today is Tuesday.";
} elseif ($day === "Wednesday") {
  echo "Today is Wednesday.";
} elseif ($day === "Thursday") {
  echo "Today is Thursday.";
} elseif ($day === "Friday") {
  echo "Today is Friday.";
} elseif ($day === "Saturday") {
  echo "Today is Saturday.";
} elseif ($day === "Sunday") {
  echo "Today is Sunday.";
} else {
  echo "Unknown day.";
}

Switch statement example

Here's the same example but with a switch statement in PHP:

In this example, the switch statement uses the variable $day. The switch statement then compares the value of $day to the different case values and prints a message based on the matching case. If no matching case is found, the default case is executed.

$day = "Monday";
 
switch ($day) {
  case "Monday":
    echo "Today is Monday.";
    break;
  case "Tuesday":
    echo "Today is Tuesday.";
    break;
  case "Wednesday":
    echo "Today is Wednesday.";
    break;
  case "Thursday":
    echo "Today is Thursday.";
    break;
  case "Friday":
    echo "Today is Friday.";
    break;
  case "Saturday":
    echo "Today is Saturday.";
    break;
  case "Sunday":
    echo "Today is Sunday.";
    break;
  default:
    echo "Unknown day.";
    break;
}

Alternative syntax

Alternatively, you can use the following syntax to produce a switch statement. Instead of using curly brackets, you can use the endswitch keyword to denote the end of the statement.

$day = "Monday";
 
switch ($day) :
  case "Monday":
    echo "Today is Monday.";
    break;
  case "Tuesday":
    echo "Today is Tuesday.";
    break;
  case "Wednesday":
    echo "Today is Wednesday.";
    break;
  case "Thursday":
    echo "Today is Thursday.";
    break;
  case "Friday":
    echo "Today is Friday.";
    break;
  case "Saturday":
    echo "Today is Saturday.";
    break;
  case "Sunday":
    echo "Today is Sunday.";
    break;
  default:
    echo "Unknown day.";
    break;
endswitch;

Fall-through behavior

In programming, "fall-through" behavior specifically relates to switch statements.

In a switch statement, you can have multiple case blocks, each representing a different condition. When the switch statement is run, it checks each case one by one until it finds one that matches. When a match is found, it starts executing the code inside that case.

Now, here's where "fall-through" comes in. If a case doesn't end with a break statement, the program doesn't stop at the end of that case. Instead, it "falls through" to the next case and starts executing the code there, even if the case condition doesn't match. It'll keep doing this, executing code from subsequent case blocks until it hits a break statement or runs out of case blocks.

Here's an example to illustrate:

$fruit = "Apple";
 
switch ($fruit) {
  case "Apple":
    echo "You chose Apple. ";
  case "Banana":
    echo "You chose Banana. ";
  case "Cherry":
    echo "You chose Cherry. ";
    break;
}

In this example, if $fruit is "Apple", you might expect it to just echo "You chose Apple.". However, because of the fall-through behavior (lack of break statements after "Apple" and "Banana"), it will actually echo "You chose Apple. You chose Banana. You chose Cherry."

In general, you need to be careful with fall-through behavior. It can be useful in some scenarios where you want multiple case conditions to execute the same block of code, but it can also lead to unexpected results if you forget to include a break statement.

Here's an example to illustrate this:

$fruit = "Apple";
 
switch ($fruit) {
  case "Apple":
  case "Banana":
  case "Cherry":
    echo "This is a common fruit.";
    break;
  case "Dragonfruit":
  case "Kumquat":
    echo "This is an exotic fruit.";
    break;
  default:
    echo "I don't know this fruit.";
    break;
}

In the example above, if $fruit is "Apple", "Banana", or "Cherry", the code will echo "This is a common fruit.". This happens because when the switch statement finds a matching case, it executes all code until it hits a break statement. In this case, since there's no break after "Apple" or "Banana", it will "fall through" to the next case until it finds a break.

Similarly, if $fruit is "Dragonfruit" or "Kumquat", the code will echo "This is an exotic fruit.".

If $fruit is anything else, it will go to the default case and echo "I don't know this fruit.". The default case serves as a fallback if no other cases match.

The break keyword is crucial in a switch statement, because it tells PHP to exit the switch block and not execute any more code within it. If you omit the break, PHP will continue to execute the next case or default block, even if it doesn't match the condition, which can lead to unexpected results.

if vs switch

The switch and if statements are both used to conditionally execute code in PHP, but there are a few key differences between the two:

  1. Syntax: The syntax for a switch statement is more compact than the equivalent if statement. A switch statement only requires a single expression to be evaluated, followed by a series of case statements that determine what code to execute. An if statement, on the other hand, requires a complete if condition to be written for each possible outcome.
  2. Speed: switch statements are generally faster than if statements when evaluating a large number of conditions. This is because switch statements are optimized for this type of evaluation, whereas if statements require a series of condition evaluations.
  3. Readability: switch statements can make code more readable, especially when there are a large number of conditions to evaluate. The case statements in a switch statement are clearly labeled, making it easy to see what code will be executed in each case. With an if statement, it can become difficult to understand the code when there are many nested if conditions.

In general, you would use a switch statement when you have a large number of conditions to evaluate, and the conditions are easily represented as a series of discrete outcomes. You would use an if statement when you have a smaller number of conditions to evaluate, and the conditions are more complex and cannot be easily represented as discrete outcomes.

Exercises

Exercise #1

Create a simple program that outputs the name of the month based on the number. For example, if the number is 3, the month will be March.

Exercise #2

Rewrite the "switch" into an "if". Write the code using if..else, which would correspond to the following switch:

switch ($browser) {
  case 'Edge':
    echo "You've got the Edge!";
    break;
  case 'Chrome':
  case 'Firefox':
  case 'Safari':
  case 'Opera':
    echo 'Okay we support these browsers too';
    break;
  default:
    echo 'We hope that this page looks ok!';
}

Exercise #3

Rewrite the code below using a single switch statement:

$a = 1;
 
if ($a == 0) {
  echo 0;
}
if ($a == 1) {
  echo 1;
}
 
if ($a == 2 || $a == 3) {
  echo '2,3';
}

Key takeaways

  • The switch statement can be useful when comparing two values as opposed to using the if statement.
  • Inside a switch statement, we can provide a list of values to compare with by using the case keyword.
  • If a match can't be found, a fallback can be provided with the default keyword.
  • Use the break keyword to prevent the rest of the switch statement from running.
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Flow Control
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Match Expression

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