C ProgrammingC Programming

Lecture 11Lecture 11

The The switchswitch Statement Statement

The The switchswitch statement is a statement is a multiway conditional multiway conditional statement statement generalizinggeneralizing the the if-elseif-else statement. statement.

switchswitch switch (expression){ case constant1: statement

. . .statement

case constant_2: statement. . .statement

case constant_n: statement. . .statement

default : statement. . .statement

} /* end switch */

The The breakbreak Statement Statement

The The breakbreak statement causes a statement causes a jump out of a switch jump out of a switch statement.statement.• Execution continues after the Execution continues after the closing brace of the switch closing brace of the switch statement.statement.

Example Using the Example Using the switchswitch StatementStatement

switch (val) { case 1: ++a_cnt; break; case 2: case 3: ++b_cnt; break; default: ++other_cnt;}

The val expression mustbe of an integer type.

The constant integralexpressions following thecase labels must all be unique.

The Effect of a The Effect of a switch switch StatementStatement

EvaluateEvaluate the switch the switch expressionexpression.. Go to the Go to the case labelcase label having a having a constant constant valuevalue that matches the value of the that matches the value of the expression found in step 1.expression found in step 1.• If a match is not found, go to the If a match is not found, go to the default labeldefault label..

• If there is no default label, If there is no default label, terminate the switch.terminate the switch.

Terminate the switch when a Terminate the switch when a breakbreak statement is encountered, statement is encountered, oror by by “falling off the end”.“falling off the end”.

Bell Labs Industrial Bell Labs Industrial Programming StyleProgramming Style

Follow normal rules of English, where Follow normal rules of English, where possible.possible.• e.g., put a space after a commae.g., put a space after a comma

Put one space on either side of a Put one space on either side of a binary operator.binary operator.

Indent code in a consistent fashion to Indent code in a consistent fashion to indicate flow of control.indicate flow of control.

Put braces as indicated in the Put braces as indicated in the following example:following example: for (i = 0; i < n; ++i) for (i = 0; i < n; ++i) {{ . . . . . . /* indent 3 spaces *//* indent 3 spaces */ }}

Student StyleStudent Style

Place Place beginningbeginning and ending and ending braces in the same column.braces in the same column. while (i < 10)while (i < 10)

{{

. . .. . .

}} Either style for braces is Either style for braces is acceptable in our class.acceptable in our class.

Misuse of Relational Misuse of Relational OperatorsOperators

int k = 8;int k = 8;if (if (2 < k < 72 < k < 7)) printf(“true”); printf(“true”); /*true is printed*//*true is printed*/elseelse printf(“false”);printf(“false”);

int k = 8;int k = 8;if (if (2 < k && k <2 < k && k < 7) 7) printf(“true);printf(“true);elseelse printf(“false”); printf(“false”); /*false is printed*//*false is printed*/