CZ1102 Computing & Problem Solving Lecture 3

8/8/2019 CZ1102 Computing & Problem Solving Lecture 3

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Relationoperationandconditional

statement

Week4

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Logicalexpression Evaluatethecorrectnessofthestatement

TRUE

FALSE

Sixrelationshipoperator

1. == equal

2. ~= notequal

3. > greaterthan

4. >= greaterthanorequalto

5.


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(cont) Examples

b2


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Logicaloperator

logicaloperators

~:

not&:and

|: or

Example>>1&0

ans =

0

>>

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Operatorprecedence

Precedence(fromthefirsttothelast)

Parenthesis

() Arithmeticoperators

Relationshipoperators

==,~=,>,>=,


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(cont)

Example

>>2>1&0ans=

0

Danger

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(cont) Wrongway

>>0(0


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AssignmentofLogicalexpression

Example

x

=

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Conditionalstatement

Decisionexample1

Considerthefollowingarithmeticoperationonx

The aboveoperationmustdecidewhetherornotx

ispositiveornot.Theifconstruct,whichisfundamentaltoallcomputinglanguages,isthebasis

ofsuchdecisionmaking.

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Theonelineif statement ifcondition

statement

end

conditionisusuallyalogicalexpression Ifconditionistrue,statementisexecuted,butifconditionisfalse,

nothinghappens.

Samplecode

>>x=3>>if(x>xx=

3

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Decisionexample2 Example

Considerthefollowingarithmeticoperationonx

1, 01, ifcondition

statementA

elsestatementB

end

conditionisusuallyalogicalexpression Ifconditionistrue,statementA isexecuted,butifconditionisfalse,statementB isexecuted. Dontforgetend,orMATLABwillwaitforever.

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Samplecode Thecode

>>x=3

>>if(x>=0)

x=1;

else

x=1;

end

>>x

x=

1

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elseif ladder ifcondition1

statementsA

elseifcondition2

statementsB

elseifcondition3

statementsC

else

statementsE

end

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Howdoesitwork condition1istested.Ifitistrue,statementsA areexecuted;MATLAB

thenmovestothenextstatementafterend.

Ifcondition1isfalse,MATLABcheckscondition2.Ifitistrue,statementsB

areexecuted,followedbythestatementafterend.

Inthisway,alltheconditionsaretesteduntilatrueconditionisfound.

Assoonasatrueconditionisfound,nofurtherelseifs areexamined,

and MATLABjumpsofftheladder.

Ifnoneoftheconditionsistrue,statementsEafterelseareexecuted.

Youshouldarrangethelogicsothatnotmorethanoneofthe

conditions istrue.

Therecanbeanynumberofelseifs,butatmostoneelse.

elseifmustbewrittenasoneword.14


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Example Code

>>if(x>0)

x=1;

elseif (x=0)

x=0;else

x=1;

end Whatthisconditionalstatementdoes?

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Multipleifsvs elseif Casestudy:Theinterestrateofthebankisgivenas

following

Ifsavingisbetween[0,5000),rateis0.01

Ifsavingisbetween[5000,10000),rateis0.015

If

saving

>=10000,

rate

is

0.02.

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Samplecode>>ifsaving


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Wrongcodeusingmultipleifs>>ifsaving


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Correctoneusingmuiple ifs.>>ifsaving=5000&saving=10000;

rate

=0.02;end

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Nestedifs Anifconstructcancontainfurtherifs,andsoon.

ifcondition1

statementsA

ifcondition2statementsB

elsestatementsC

end

else

statementD

end

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Example Example

Find

one

real

root

of

,

Thesolutionis

If c/b

Otherwise

If 4 0, (or

) Otherwise,complexrootsonly

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Samplecode >>if(a==0)

x= b/c;

else

if(b^24*a*c>0)

x=(b+sqrt(b^24*a*c)/(2*a);

elsedisp (norealroot);

end;

end;

Itisgoodprogrammingstyletoindenteachgroupofstatementsasshown.

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Switchstruct Theswitch statementexecutescertainstatementsbasedonthevalueofa

variableorexpression.

switch Variablecase valueA

statementA;

case valueB

statementB0;

casevalueEstatementE;

otherwise

statementF;

end

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Switchstruct Example:Rollingdiceincasino,

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Usingswitch

struct

Samplecode

>> D%denotethedicenumber

switchD

case1pay=50;

case2

pay=20;

case3

pay=10;case4

pay=5;

case5

pay=10;

otherwisepay=25;

end

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CZ1102 Computing & Problem Solving Lecture 3