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Selection Statements Conditional Expression... Selection Statements Conditional ExpressionSelection Criteria Selection criteria = value of expression ⇒ select appropriate flow of control

Selection Statements

Conditional Expression

C++ Selection Structures

Department of Computer Science

HCMC University of Technology, Viet Nam

02, 2014

Selection Statements Conditional Expression

Selection Statements Conditional Expression

yes no

Selection Statements Conditional Expression

Selection Criteria

Selection criteria = value of expression ⇒ select appropriate flow of control

C++

if statement: 2 values (true/false, 0/not 0)

switch statement: multiple discrete values

Selection Statements Conditional Expression

Relational Operators

used to compare 2 operands

return Boolean value (true/false) (i.e bool type)

Selection Statements Conditional Expression

Logical Operators

used to create more complex conditions

its operands in bool type

also return bool value

short-circuit evaluation

Selection Statements Conditional Expression

Operator Precedence and Associativity

List in the decreasing order of the precedence

Selection Statements Conditional Expression

Selection Statements Conditional Expression

Order of evaluation for Arithmetic/Relational Expression

Higher precedence operators are evaluated before lower precedence operator

Selection Statements Conditional Expression

Order of evaluation for Logical Expression

Short-circuit evaluation

&&: if the left operand is false ⇒ stop and return false

||: if the left operand is true ⇒ stop and return true

Selection Statements Conditional Expression

The bool data type

C++ uses bool for Boolean type

The actual value of true is 1 and false is o

The if-else statement

directs the computer to

select a statement based

no

taxable income greater

than $20,000, taxes are

2.5% of the income that

exceeds $20,000 plus a

fixed amount of $400

StartInput taxable

taxable > CUTOFF

taxes = HIGHRATE * (taxable - CUTOFF) + FIXEDAMT

taxes= LOWRATE

* taxable

Output taxesEnd

yes

no

Please t y p e i n t h e t a x a b l e income : 30000Taxes are $ 650

no

Selection Statements

Conditional Expression

If Statement

Switch Statement

Solve dangling else

Use block statement

if (exp1) {if (exp2) stmt1} else stmt2

if (exp1) {if (exp2) stmt1 else stmt2}

Use C++ convention: else matches with closest unmatch if

statement

is based on the value of an expression

requires the expression in int type

Syntax:

switch ( < e x p r e s s i o n >) {

case < v a l u e 1 >: [ < statements > ]

[ break ; ] case < v a l u e 2 >: [ < statements > ]

[ break ; ] case < v a l u e 3 >: [ < statements > ]

is based on the value of an expression

requires the expression in int type

Syntax:

switch ( < e x p r e s s i o n >) {

case < v a l u e 1 >: [ < statements > ]

[ break ; ] case < v a l u e 2 >: [ < statements > ]

[ break ; ] case < v a l u e 3 >: [ < statements > ]

[ d e f a u l t : < s ta te men ts > ]

Then, compare to <value 1>

is based on the value of an expression

requires the expression in int type

Syntax:

switch ( < e x p r e s s i o n >) {

case < v a l u e 1 >: [ < statements > ]

[ break ; ] case < v a l u e 2 >: [ < statements > ]

[ break ; ] case < v a l u e 3 >: [ < statements > ]

[ d e f a u l t : < s ta te men ts > ]

}

If match,execute <statements>

is based on the value of an expression

requires the expression in int type

Syntax:

switch ( < e x p r e s s i o n >) {

case < v a l u e 1 >: [ < statements > ]

[ break ; ] case < v a l u e 2 >: [ < statements > ]

[ break ; ] case < v a l u e 3 >: [ < statements > ]

[ d e f a u l t : < s ta te men ts > ]

If not match, compare to <value 2>

is based on the value of an expression

requires the expression in int type

Syntax:

switch ( < e x p r e s s i o n >) {

case < v a l u e 1 >: [ < statements > ]

[ break ; ] case < v a l u e 2 >: [ < statements > ]

[ break ; ] case < v a l u e 3 >: [ < statements > ]

is based on the value of an expression

requires the expression in int type

Syntax:

switch ( < e x p r e s s i o n >) {

case < v a l u e 1 >: [ < statements > ]

[ break ; ] case < v a l u e 2 >: [ < statements > ]

[ break ; ] case < v a l u e 3 >: [ < statements > ]

[ d e f a u l t : < s ta te men ts > ]

If there is break,

go out of switch

is based on the value of an expression

requires the expression in int type

Syntax:

switch ( < e x p r e s s i o n >) {

case < v a l u e 1 >: [ < statements > ]

[ break ; ] case < v a l u e 2 >: [ < statements > ]

[ break ; ] case < v a l u e 3 >: [ < statements > ]

Selection Statements

Conditional Expression

Conditional Expression

There are 3 argument expressions

If the value of the first expression is true, evaluate and return the value of the second expression.

Otherwise, evaluate and return the value of the third.

Selection Statements

Conditional Expression

Summary

Relational and logical expression

If-Else and If-No-Else statement

Nested if statement

Switch statement

Conditional Expression