switch case

Definition

The switch case statement is used to select one of many blocks of code to be executed.

It is an alternative way to create a multiway branch (instead of using if else).

Syntax

switch case

A simple switch case statement has the following syntax:

• JavaScript
• Java
• Python

switch (expression) {
    case value1:
        // code to execute if expression matches value1
        break;	// optional	break
    case value2:
        // code to execute if expression matches value2
        break;	// optional	break
    ......
    default:	// optional default
        // code to be executed if the all cases are not matched
}

switch (expression) {
    case value1:
        // code to execute if expression matches value1
        break;	// optional	break
    case value2:
        // code to execute if expression matches value2
        break;	// optional	break
    ......
    default:	// optional default
        // code to be executed if the cases are not matched
}

JavaScript and Java syntax.

• The value of the expression is compared with each case value. When there is a match, the associated code block is executed.
• The optional break keyword is used to bypass any further code in the switch case. If the break is missing, the code in any following cases will be executed even if they do not match the expression!
• The code specified within the optional default will be run if the expression does not match any of the case values.

Example - A Simple Menu

We will create a menu and use the switch case to check if a user enters 'a' to add, 's' to subtract or 'q' to Quit.

JavaScript and Java example.

1. We assign 's' to the variable option and check if this matches one of the cases. We will also test how the switch runs when the break keyword is not included.
• JavaScript
• Java
• Python

var option = 's'; 

switch (option) {
    case 'a':
        alert("Add selected");
    case 's':
        alert("Subtract selected");
    case 'q':
        alert("Quit selected");		  
    default:	
        alert("Incorrect input");
}

JavaScript Notes: We use the JavaScript alert() popup window to let the user know the output of the switch case. Although the alert() can be annoying to users it is good for initial testing while developing this example.

char option = 's';  
 	
switch (option) {
    case 'a':
        System.out.println("Add selected");
    case 's':
        System.out.println("Subtract selected");
    case 'q':
        System.out.println("Quit selected");	  
    default:	
         System.out.println("Incorrect input");
}

Java Note: Java uses single quotes for char and double quotes for strings.

Python Note: The switch case is not supported by Python.

When run, the value in option matches the 's' of the second case and executes the associated code to display the message 'Subtract selected.'

However, when a match is found, any remaining code in the switch will be executed until either a break is found or the end of the switch is reached. Even although the option value does not match the remaining cases, the following is displayed: 'Subtract selected', 'Quit selected', 'Incorrect input'.

There might be occasions when you want this type of logic in your program, but this example requires only the matched code to run.

2. Now we will add the break keyword so that only the code associated with the matching case will be executed. We will also ensure that our program deals with any upper case characters.
• JavaScript
• Java
• Python

var option = 'S'; 
option = option.toLowerCase();

switch (option) {   
    case 'a':
        alert("Add selected");
        break;	
    case 's':
        alert("Subtract selected");
        break;	
    case 'q':
        alert("Quit selected");
        break;		  
    default:	
        alert("Incorrect input");
}

JavaScript Note: The variable option is a string. The toLowerCase() method returns a new string with any upper case letters converted to lower case letters.

char option = "S";
option = Character.toLowerCase(option);

switch (option) {
    case 'a':
        System.out.println("Add selected");
        break;	
    case 's':
        System.out.println("Subtract selected");
        break;	
    case 'q':
        System.out.println("Quit selected");
        break;	  
    default:	
         System.out.println("Incorrect input");
}

Java Note: The variable option is a char. Line 2 uses Character.toLowerCase() method to return the lower case equivalent of the character, if any, or the character itself.

Python Note: The switch case is not supported by Python.

As each case value is in lower case, the input value is converted to lower case prior to testing for a match in the switch case.

If a case match is found, the associated code block is executed. Any further code in the following cases is ignored as the keyword break is used.

The code specified within the default will be run if the users input does not match one of the case values. A break is not required within the default block as it is the last block of the switch.

3. We will now get the input from the user and store it in the option variable. We will also store the outcome of the switch case match in a variable selection to be used later in the program.
• JavaScript
• Java
• Python

var option, selection; 
option = prompt("Enter 'a' to Add, 's' to Subtract, 'q' to Quit");
option = option.toLowerCase();

switch (option) {
    case 'a':
        selection = "Add";
        break;	
    case 's':
        selection = "Subtract";
        break;	
    case 'q':
        selection = "Quit";
        break;		  
    default:	
        selection = "Incorrect input";
}
document.write(selection);

JavaScript Notes:

We use the JavaScript prompt() popup window to get input from the user and save the string input into the variable option.

We have replaced the alert() popup window with a document.write() method to display the value stored in the variable selection.

char option;
String selection;
  
Scanner input = new Scanner(System.in);
  
System.out.println("Enter 'a' to Add, 's' to Subtract, 'q' to Quit");
option = input.next().charAt(0); 
option = Character.toLowerCase(option);

switch (option) {
    case 'a':
        selection = "Add";
        break;	
    case 's':
        selection = "Subtract";
        break;	
    case 'q':
        selection = "Quit";
        break;	  
    default:	
        selection = "Incorrect input";
}
System.out.println(selection);

Java Notes:

Remember to import the Scanner at the start of your Java program (not shown in this example - import java.util.Scanner). The Scanner allows us to create an object to enable keyboard input. Here, the object is named input:

•    Scanner input = new Scanner(System.in);

The input object allows access to the next() method to get the next word in the input. The charAt(0) function returns the first character in that string:

•     char option = input.next().charAt(0);

Python Note: The switch case is not supported by Python.

The examples now get input from the user and save the input into the variable option.

We store the result of the switch case into the variable selection and display this at the end of the code.