Switch – Case Statements

By: Er. Aman Kumar

Switch-Case Statements

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• Switch case statement allows us to make decisions from multiple choices.

• Integer expression must yield an integer value like 1, 2, 3, etc. The keyword case is followed by an integer or a character constant.

• Each constant in each case must be different from all the others. The “do this” lines in the above form of switch represent any valid C statement.

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• break always used with the switch statement to terminate the switch statement or to prevent the entry in other case.

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The Tips and Traps

• It is not compulsory to put cases in ascending order as we did above. We can place them in any order we want.

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You are also allowed to use char values in case and switch as

shown in the following program

(Program to find whether character entered is vowel or not)

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Modified

Form

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If a statement doesn’t belong to any case the compiler won’t report an error. However, the statement would

never get executed. For example, in the following program the printf( ) never goes to work.

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• If there is no default in switch, then error will not be there. If no case is matching, statements after switch will execute.

• Relational Expression like i>5 are not allowed in any case. Even float values not allowed in any case

• We can check the value of any expression in a switch. Thus the following switch statements are legal.

switch ( i - j * k )

switch ( 3 + 9 % 4 * i )

switch ( a < 5 || b > 7 )

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• Expressions can also be used in cases provided they are constant expressions. Thus case 13 + 7 is correct, however, case a + b is incorrect.

• switch may occur within another, but in practice it is rarely done. Such statements would be called nested switch statements.

• The switch statement is very useful while writing menu driven programs

• Even if there are multiple statements to be executed in each case there is no need to enclose them within a pair of braces (unlike if, and else).

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switch Versus if-else Ladder

Disadvantages of switch over if-else

• A float expression cannot be tested using a switch

• Cases can never have variable expressions (for example it is wrong to say case a +3 : )

• Multiple cases cannot use same expressions. Thus the following switch is illegal:

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Advantages of switch over if-else

• compiler generates a jump table for a switch during compilation. As a result, during execution it simply refers the jump table to decide which case should be executed, rather than actually checking which case is satisfied.

• As against this, if-else are slower because they are evaluated at execution time.

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