Code Snippets (Conditional Statements)

8/3/2019 Code Snippets (Conditional Statements)

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Conditional StatementsConditional Statements

Prepared by: Eisen SyPrepared by: Eisen Sy


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Conditional StatementConditional Statement

Conditional statements allow yourConditional statements allow yourprogram to make a decision based on aprogram to make a decision based on a

setofconditions.setofconditions. Conditional statements in C# may beConditional statements in C# may be

implemented using theimplemented using the IfIfstatementstatement..

Conditional statements have variousConditional statements have variousstructures which we will study in the nextstructures which we will study in the nextslide.slide.


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Conditional Statement StructuresConditional Statement Structures

IfstatementIfstatement IfIf Else statementElse statement IfIf Else IfstatementElse Ifstatement Switch statementSwitch statement


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IfStatementIfStatement

The first type ofThe first type ofifstatementifstatementallows our programallows our programto perform a setof instructions ifa certainto perform a setof instructions ifa certain

condition iscondition is truetrue.. This type ofThis type ofifstatementifstatementsimply proceeds to thesimply proceeds to the

next instruction should the condition of thenext instruction should the condition of the ififstatementstatementturned out to beturned out to be falsefalse..

This is the most basic form ofThis is the most basic form ofifstatementifstatement..


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IfStatementIfStatement

Syntax:Syntax:

if ( Boolean Condition )if ( Boolean Condition )

{{

True embeddedTrue embedded--statements;statements;

}}

Note: Using the curly brackets allowus towriteNote: Using the curly brackets allowus towritemore than 1 statementof instructions.more than 1 statementof instructions.


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IfStatement TipIfStatement Tip

Syntax:Syntax:


{{


}}

If Statementmust not end witha semicolon ( ; )

Embedded-Statementhowever, must end witha semicolon ( ; )


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More IfStatement TipMore IfStatement Tip

Syntax:Syntax:


{{


}}

Indentions is not required but is considered a goodprogramming habit to promote code readability.


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IfStatement ExampleIfStatement Example

Code:Code:string password;string password;

Console.Write (Input Password : );Console.Write (Input Password : );

password = Console.ReadLine ();password = Console.ReadLine ();

if ( password == wind )if ( password == wind )

{{

Console.Write (Access Granted!);Console.Write (Access Granted!);

}}

Console.ReadKey(true);Console.ReadKey(true);

Output:Output:Input Password :Input Password :windwind

Access Granted!Access Granted!


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Code:Code:string password;string password;

Console.Write (Input Password : );Console.Write (Input Password : );

password = Console.ReadLine ();password = Console.ReadLine ();

if ( password == wind )if ( password == wind )

{{

Console.Write (Access Granted!);Console.Write (Access Granted!);

}}


Output:Output:Input Password :Input Password : earthearth


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IfStatementfor 1 EmbeddedIfStatementfor 1 Embedded

StatementStatementSyntax:Syntax:



Note: Without the curly brackets, only oneNote: Without the curly brackets, only onestatement may be executed if thestatement may be executed if thecondition is true.condition is true.


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Code:Code:string name;string name;

Console.Write (Please write your name : );Console.Write (Please write your name : );

name = Console.ReadLine ();name = Console.ReadLine ();

if ( name == Eisen )if ( name == Eisen )

Console.Write (Hello Boss.Console.Write (Hello Boss.\\n);n);

Console.Write (This is the Demo Program.);Console.Write (This is the Demo Program.);


Output:Output:Please write your name :Please write your name : EisenEisen

Hello Boss.Hello Boss.

This is the Demo Program.This is the Demo Program.


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Code:Code:string name;string name;

Console.Write (Please write your name : );Console.Write (Please write your name : );

name = Console.ReadLine ();name = Console.ReadLine ();

if ( name == Eisen )if ( name == Eisen )

Console.Write (Hello Boss.Console.Write (Hello Boss.\\n);n);

Console.Write (This is the Demo Program.);Console.Write (This is the Demo Program.);


Output:Output:Please write your name :Please write your name :MikeMike

This is the Demo Program.This is the Demo Program.


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IfIf Else StatementElse Statement

This type of Ifstatement allows theThis type of Ifstatement allows theprogram to execute 2 instructions, one setprogram to execute 2 instructions, one set

of instructions if the condition isof instructions if the condition is truetrue andandanother if the condition isanother if the condition is falsefalse..


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IfIf Else StatementElse Statement

Syntax:Syntax:if ( Boolean Condition )if ( Boolean Condition )

{{

True embeddedTrue embedded--statements;statements;}}

elseelse

{{

False embeddedFalse embedded--statements;statements;

}}

Note: The rule ofcurly brackets applies in a similar way.Note: The rule ofcurly brackets applies in a similar way.


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IfIf Else Statement ExampleElse Statement Example

Code:Code:Console.Write (Input Grade : );Console.Write (Input Grade : );

int grade = int.Parse ( Console.ReadLine() );int grade = int.Parse ( Console.ReadLine() );

if ( grade >= 70 )if ( grade >= 70 )

{{

Console.Write (You Passed);Console.Write (You Passed);

}}

elseelse

{{

Console.Write (You Failed);Console.Write (You Failed);

}}


Output:Output:Input Grade :Input Grade : 8080

You PassedYou Passed


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if ( grade >= 70 )if ( grade >= 70 )

{{


}}

elseelse

{{


}}



You FailedYou Failed


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IfIf Else Statement (Alternative)Else Statement (Alternative)

Syntax:Syntax:


True embeddedTrue embedded--statements;statements;elseelse

False embeddedFalse embedded--statements;statements;

Note: Without the curly braces, onlyNote: Without the curly braces, only 1 embedded1 embeddedstatementstatementmay be inserted per section of themay be inserted per section of the IfIfstatementstatement..


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if ( grade >= 70 )if ( grade >= 70 )


elseelse




You PassedYou Passed


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if ( grade >= 70 )if ( grade >= 70 )


elseelse




You FailedYou Failed


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IfIf Else IfStatementElse IfStatement

This type of Ifstatement allows us toThis type of Ifstatement allows us tospecify multiple conditions.specify multiple conditions.


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IfIf Else IfStatementElse IfStatement

Syntax:Syntax:if ( Boolean Condition A )if ( Boolean Condition A )

{{

EmbeddedEmbedded--Statements for Condition AStatements for Condition A;;

}}

else if ( Boolean Condition B )else if ( Boolean Condition B ){{

EmbeddedEmbedded--Statements for Condition BStatements for Condition B;;

}}

else if ( Boolean Condition C )else if ( Boolean Condition C )

{{

EmbeddedEmbedded--Statements for Condition CStatements for Condition C;;

}}

elseelse{{

EmbeddedEmbedded--Statements for Conditions not metStatements for Conditions not met;;

}}

Note: You can have variable number ofconditions when using this type ofNote: You can have variable number ofconditions when using this type ofIfstatementIfstatement..


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Sample Code:Sample Code:Console.Write (Input Age : );Console.Write (Input Age : );

int age = int.Parse ( Console.ReadLine() );int age = int.Parse ( Console.ReadLine() );

if ( age >= 0 && age = 0 && age = 21 && age = 21 && age = 51 && age = 51 && age


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Output Sample 1:Output Sample 1:

Input Age :Input Age : 3737

Youre an adult.Youre an adult.

Output Sample 2:Output Sample 2:

Input Age :Input Age : 2020

Youre still young.Youre still young.

Output Sample 3:Output Sample 3:Input Age :Input Age : 9090

Youre old.Youre old.


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Switch StatementSwitch Statement

Switch statementSwitch statementis an alternative tousing Ifis an alternative tousing IfElse Ifstatement.Else Ifstatement.

Switch statementSwitch statementevaluate the value ofa certainevaluate the value ofa certainvariable usingvariable usingcasescases..

AA break statementbreak statementallows the program to exitallows the program to exitthe entirethe entire switch statementswitch statementsection.section.

Thus, aThus, a break statementbreak statementprevents a case ofaprevents a case ofaswitch statementswitch statementfrom moving to the next case.from moving to the next case.


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Syntax:Syntax:switch (variable)switch (variable)

{{

case A:case A:

Embedded statements if variable is A;Embedded statements if variable is A;

break;break;

case B:case B:

Embedded statements if variable is B;Embedded statements if variable is B;

break;break;

case C:case C:

Embedded statements if variable is C;Embedded statements if variable is C;

break;break;default:default:

Statements if variable is other than A, B or C;Statements if variable is other than A, B or C;

break;break;

}}


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Switch Statement TipsSwitch Statement Tips


{{

case A:case A:


break;break;

case B:case B:


break;break;

case C:case C:




break;break;

}}

No Semi-colon ( ; )


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{{

case A:case A:


break;break;

case B:case B:


break;break;

case C:case C:




break;break;

}}

Enclosed in CurlyBraces { }


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{{

case A:case A:


break;break;

case B:case B:


break;break;

case C:case C:




break;break;

}}

Use Colons forcases ( : )


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{{

case A:case A:


break;break;

case B:case B:


break;break;

case C:case C:




break;break;

}}

Use break for allcases


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When usingWhen usingstringstring data types, case valuesdata types, case valuesare enclosed inare enclosed in double quotes ( )double quotes ( )..

Cases areCases are not enclosednot enclosed when usingwhen usingnumericnumeric data types.data types.


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Code:Code:Console.Write (Input A, B or C : );Console.Write (Input A, B or C : );

string choice = Console.ReadLine ();string choice = Console.ReadLine ();

switch (choice)switch (choice){{

case A:case A:

Console.Write (You selected A.);Console.Write (You selected A.);

break;break;

case B:case B:Console.Write (You selected B.);Console.Write (You selected B.);

break;break;

case C:case C:

Console.Write (You selected C.);Console.Write (You selected C.);

break;break;

default:default:Console.Write (Invalid Input!);Console.Write (Invalid Input!);

break;break;

}}



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Output Sample 1:Output Sample 1:Input A, B or C :Input A, B or C :AA

You selected A.You selected A.

Output Sample 2:Output Sample 2:Input A, B or C :Input A, B or C : BB

You selected B.You selected B.

Output Sample 3:Output Sample 3:Input A, B or C :Input A, B or C : CC

You selected C.You selected C.

Output Sample 4:Output Sample 4:Input A, B or C :Input A, B or C : DD

Invalid Input!Invalid Input!


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Code:Code:Console.Write (Input 1, 2 or 3 : );Console.Write (Input 1, 2 or 3 : );

int choice = int.Parse ( Console.ReadLine() );int choice = int.Parse ( Console.ReadLine() );

switch (choice)switch (choice){{

case 1:case 1:

Console.Write (One!);Console.Write (One!);

break;break;

case 2:case 2:Console.Write (Two!!);Console.Write (Two!!);

break;break;

case 3:case 3:

Console.Write (Three!!!);Console.Write (Three!!!);

break;break;

default:default:Console.Write (Invalid Input!!!!);Console.Write (Invalid Input!!!!);

break;break;

}}



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Output Sample 1:Output Sample 1:Input 1, 2 or 3 :Input 1, 2 or 3 : 11

One!One!


Two!!Two!!


Three!!!Three!!!


Invalid Input!!!!Invalid Input!!!!


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DEMO Programs for the LessonDEMO Programs for the Lesson

1.1. Avoiding division by zero in a divide operationAvoiding division by zero in a divide operation2.2. Checking textboxes for empty in a summationChecking textboxes for empty in a summation

programprogram3.3. Validating numerical entries in a problemValidating numerical entries in a problem

similar to item 1similar to item 1

4.4. Retrievinguser response in a message boxRetrievinguser response in a message box5.5. Check ifusername is not empty andCheck ifusername is not empty and passwordpassword

has minimumhas minimum of7 charactersof7 characters


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The End. Thank youfor listening.The End. Thank youfor listening.

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Code Snippets (Conditional Statements)