Rules of Using Switch Case in C Programming
- Case Label must be unique
- Case Labels must ends with Colon
- Case labels must have constants / constant expression
- Case label must be of integral Type ( Integer,Character)
- Case label should not be ‘floating point number ‘
- Switch case should have at most one default label
- Default label is Optional
- Default can be placed anywhere in the switch
- Break Statement takes control out of the switch
- Two or more cases may share one break statement
- Nesting ( switch within switch ) is allowed.
- Relational Operators are not allowed in Switch Statement.
- Macro Identifier are allowed as Switch Case Label.
- Const Variable is allowed in switch Case Statement.
- Empty Switch case is allowed.
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; }
