Switch-Case statement (Glossary Entry)

A switch-case is used for flow control when you are testing the same variable for equality.

switch (expression) {

<declarations>

case constant:

statements

break;

case constant:

statements

break;

default:

statements

break;

}

 

The term ‘expression’ above refers to a variable under test. From the diagram below, it is the selector that is used to determine the flow of code within the switch-case statement.

Consider the following example:

int iResponse;

puts("Please select:");
puts("0 - Sales");
puts("1 - Opening hours");
puts("2 - Repairs");
puts("3 - Complaints");
puts("4 - Anything else");

scanf("%d", &iResponse);

if (iResponse == 0) {
   puts("Please wait for a sales advisor");
   playAnnoyingMusic(5);
   redirect(123);
} else if (iResponse == 1) {
   puts("We are open 24Hrs 7 days a week");
   redirect(0);
} else if (iResponse == 2) {
   puts("Please wait while we redirect you");
   playAnnoyingMusic(25);
   redirect(124);
} else if ((iResponse == 3) || (iResponse == 4)) {
   puts("Please wait while we redirect you");
   playAnnoyingMusic(60);
   redirect(0);	//very cynical
} else {
   puts("Returning to main menu");
   playAnnoyingMusic(5);
   redirect(0);	//very cynical
};

Note how it is the same variable being tested each time. The equivalent code with a switch-case is as follows:

int iResponse;

puts("Please select:");
puts("0 - Sales");
puts("1 - Opening hours");
puts("2 - Repairs");
puts("3 - Complaints");
puts("4 - Anything else");

scanf("%d", &iResponse);

switch (iResponse) {
      
   case 0:
      puts("Please wait for a sales advisor");
      playAnnoyingMusic(5);
      redirect(123);
      break;
   case 1:
      puts("We are open 24Hrs 7 days a week");
      redirect(0);
      break;
   case 2:
      puts("Please wait while we redirect you");
      playAnnoyingMusic(25);
      redirect(124);
      break;
   case 3:
   case 4:
      puts("Please wait while we redirect you");
      playAnnoyingMusic(60);
      redirect(0);	//very cynical
      break;
   default:
      puts("Returning to main menu");
      playAnnoyingMusic(5);
      redirect(0);	//very cynical
      break;
};

Notes:

• Each evaluation must be exclusive
• Use break  to avoid falling through into the next case (common error)
• Multiple conditions can be handled by writing separate case statements without a break.
• default  (optional) is the catch-all if none are matched