Switch Statement

Syntax of Switch Case :

switch ( expression )
    {
      case label1 :
            body1
            break;

      case label2 :
            body2
            break;

      case label3 :
            body3
            break;

      default :
           default-body
           break;
 }
 next-statement;

---

Rule 1 : Case Label must be unique

int id = 3 ;
switch(id)
       {
       case 1:
               printf("C Programming Language");
               break;
       case 2:
               printf("C++ Programming Language");
               break;
       case 2:
               printf("Web Technology");
               break;
       default :
               printf("No student found");
               break;
        }

Rule 2 : Case Labels must ends with Colon

case 1 :
       printf("C Programming Language");
       break;

Rule 3 : Case labels must have constants / constant expression

case 1+1:
case 'A':
case 67:

these are allowed examples of switch case labels , however variables are not allowed in switch case labels.

case var :
case num1 :
case n1+n2 :

Rule 4 : Case label must be of integral Type ( Integer,Character) whereas Case label should not be ‘floating point number ‘

case 10:
case 20+20:
case 'A':
case 'a':

these are allowed examples and following are illegal examples –

case 10.12:
case 7.5:

Rule 5 : Switch case should have at most one default label

switch(roll)
       {
       case 1:
               printf("C Programming Language");
               break;
       case 2:
               printf("C++ Programming Language");
               break;
       case 2:
               printf("Web Technology");
               break;
       default :
               printf("Default Version 1");
               break;
       default :
               printf("Default Version 2");
               break;
        }

It violets first rule.

Rule 6 : Default label is Optional

switch(roll)
       {
       case 1 :
               printf("C Programming Language");
               break;
       case 2 :
               printf("C++ Programming Language");
               break;
       case 2 :
               printf("Web Technology");
               break;
        }

default statement is optional. It can be neglected.

Rule 7 : Default can be placed anywhere in the switch

switch(roll)
       {
       case 1 :
               printf("C Programming Language");
               break;
       default:
               printf("No Student Found");
               break;
       case 2 :
               printf("C++ Programming Language");
               break;
       case 2 :
               printf("Web Technology");
               break;
        }

Rule 8 : Break Statement takes control out of the switch

Rule 9 : Two or more cases may share one break statement

switch(alpha)
       {
       case 'a':
       case 'A':
               printf("Alphabet A");
               break;
       case 'b':
       case 'B':
               printf("Alphabet B");
               break;
        }

Rule 10 : Nesting ( switch within switch ) is allowed

switch(alpha)
       {
       case 'a':
       case 'A':
               printf("Alphabet A");
               break;
       case 'b':
       case 'B':
               switch(alpha)
               {
               }
               break;
        }

nesting of switch case is allowed in C.

Rule 11 : Relational Operators are not allowed in Switch Statement.

switch(num)
       {
       case >15:
               printf("Number > 15");
               break;
       case =15:
               printf("Number = 15");
               break;
       case <15:
               printf("Number < 15");
               break;
        }

relational operators are not allowed as switch label.

Rule 12 : Macro Identifier are allowed as Switch Case Label.

#define MAX 2

switch(num)
       {
       case MAX:
               printf("Number = 2");
               break;
        }

as preprocessor will replace occurrence of MAX by constant value i.e 2 therefor it is allowed.

Rule 13 : Const Variable is allowed in switch Case Statement.

int const var = 2;

switch(num)
       {
       case var:
               printf("Number = 2");
               break;
        }