Switch Statement In Cpp

Switch Statement:

The switch statement checks for equality between an integer and a series of case labels, and then passes execution to the matching case. It may contain any number of case clauses and it can end with a default label for handling all other cases.

//Syntax :
switch (expression)
{
  case constant1:
  group of statements 1;
  break;
  case constant2:
  group of statements 2;
  break;
  .
  .
  .
  default:
  default group of statements
}

It works in the following way: switch evaluates expression and checks if it is equivalent to constant1, if it is, it executes group of statements 1 until it finds the break statement. When it finds this break statement the program jumps to the end of the switch selective structure.

If expression was not equal to constant1 it will be checked against constant2. If it is equal to this, it will execute group of statements 2 until a break keyword is found, and then will jump to the end of the switch selective structure.

Finally, if the value of expression did not match any of the previously specified constants (you can include as many case labels as values you want to check), the program will execute the statements included after the default: label, if it exists (since it is optional).

Both of the following code fragments have the same behavior:

The switch statement is a bit peculiar within the C++ language because it uses labels instead of blocks. This forces us to put break statements after the group of statements that we want to be executed for a specific condition. Otherwise the remainder statements -including those corresponding to other labels- will also be executed until the end of the switch selective block or a break statement is reached.

For example, if we did not include a break statement after the first group for case one, the program will not automatically jump to the end of the switch selective block and it would continue executing the rest of statements until it reaches either a break instruction or the end of the switch selective block.

This makes unnecessary to include braces { } surrounding the statements for each of the cases, and it can also be useful to execute the same block of instructions for different possible values for the expression being evaluated.

For example :

switch (x) {
case 1:
case 2:
case 3:
cout << “x is 1, 2 or 3”;
break;
default:
cout << “x is not 1, 2 nor 3”;
}

Note : Notice that switch can only be used to compare an expression against constants. Therefore we cannot put variables as labels (for example case n: where n is a variable) or ranges (case (1..3):) because they are not valid C++ constants.

If you need to check ranges or values that are not constants, use a concatenation of if and else if statements.

//Example :
#include <iostream>
using namespace std;
 
int main () {
   // local variable declaration:
   char grade = 'D';

   switch(grade) {
	  case 'A' :
		 cout << “Excellent!” << endl;
		 break;
	  case 'B' :
	  case 'C' :
		 cout << “Well done” << endl;
		 break;
	  case 'D' :
		 cout << “You passed” << endl;
		 break;
	  case 'F' :
		 cout << “Better try again” << endl;
		 break;
	  default :
		 cout << “Invalid grade” << endl;
   }
   cout << “Your grade is ” << grade << endl;
 
   return 0;
}

O/P : You passed
Your grade is D