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the if statement

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1 The if Statement The code in methods executes sequentially. The if statement allows the programmer to make decisions on whether a section of code executes or not. The if statement uses a boolean expression as an argument to decide if the next statement or block of statements executes. if(boolean expression is true) execute next statement.

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The if Statement. The code in methods executes sequentially. The if statement allows the programmer to make decisions on whether a section of code executes or not. The if statement uses a boolean expression as an argument to decide if the next statement or block of statements executes. - PowerPoint PPT Presentation

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Page 1: The if Statement

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The if Statement The code in methods executes sequentially. The if statement allows the programmer to

make decisions on whether a section of code executes or not.

The if statement uses a boolean expression as an argument to decide if the next statement or block of statements executes.if(boolean expression is true)execute next statement.

Page 2: The if Statement

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Flowcharts If statements can be modeled as a flow chart.

Wear a coat.

YesIs it coldoutside?

if (coldOutside) wearCoat();

Page 3: The if Statement

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Flowcharts A block if statement may be modeled as:

Wear a coat.

YesIs it coldoutside?

Wear a hat.

Wear gloves.

if (coldOutside){ wearCoat(); wearHat(); wearGloves();}

Note the use of curlybraces to block severalstatements together.

Page 4: The if Statement

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Relational Operators In most cases, the boolean expression, used

by the if statement, uses relational operators.

Relational Operator Meaning

> is greater than

< is less than

>= is greater than or equal to

<= is less than or equal to

== is equal to

!= is not equal to

Page 5: The if Statement

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Boolean Expressions A boolean expression is any variable or

calculation that results in a true or false condition.

Expression Meaning

x > y Is x greater than y?

x < y Is x less than y?

x >= y Is x greater than or equal to y?

x <= y Is x less than or equal to y.

x == y Is x equal to y?

x != y Is x not equal to y?

Page 6: The if Statement

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If Statements and Boolean Expressionsif (x > y)

System.out.println(“X is greater than Y”);if(x == y)

System.out.println(“X is equal to Y”);if(x != y){

System.out.println(“X is not equal to Y”);x = y;System.out.println(“However, now it is.”);

}

Page 7: The if Statement

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Programming Style and if Statements

If statements can span more than one line; however, they are still one statement.if(average > 95)

System.out.println(“That’s a great score!”);

is functionally equivalent toif(average > 95) System.out.println(“That’s a great score!”);

Page 8: The if Statement

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Programming Style and if Statements Rules of thumb:

The conditionally executed statement should be on the line after the if condition.

The conditionally executed statement should be indented one level from the if condition.

If an if statement does not have the block curly braces, it is ended by the first semicolon encountered after the if condition.if(expression)

statement;No semicolon here.Semicolon ends statement here.

Page 9: The if Statement

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Block if Statements Conditionally executed statements can be

grouped into a block by using curly braces {} to enclose them.

If curly braces are used to group conditionally executed statements, the if statement is ended by the closing curly brace.if(expression){

statement1;statement2;

} Curly brace ends the statement.

Page 10: The if Statement

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Block if Statements Remember that if the curly braces are not used, then only the next

statement after the if condition will be executed conditionally.if(expression)

statement1;statement2;statement3; Only this statement is conditionally executed.

Page 11: The if Statement

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Flags A flag is a boolean variable that monitors some

condition in a program. When a condition is true, the flag is set to a true

value. The flag can be tested to see if the condition has

changed.if(average > 95)

highScore = true; Later, this condition can be tested:

if(highScore)System.out.println(“That’s a high score!);

Page 12: The if Statement

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Comparing Characters Characters can be tested using the relational

operators. Characters are stored in the computer using the

unicode character format. Unicode is stored as a sixteen (16) bit number. Characters are ordinal, meaning they have an order

in the unicode character set. Since characters are ordinal, they can be compared

to each other.char c = ‘A’;if(c < ‘Z’)

System.out.println(“A is less than Z);

Page 13: The if Statement

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if-else Statements The if-else statement adds the ability to

conditionally execute code based if the expression of the if statement is false.

if(expression)statementOrBlockIfTrue;

elsestatementOrBlockIfFalse;

Page 14: The if Statement

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if-else Statement Flowcharts

Wear a coat.

YesIs it coldoutside?

Wear shorts.

No

Page 15: The if Statement

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if-else-if Statements if-else-if statements can become very

complex. Imagine the following decision set.

if it is very cold, wear a heavy coat,else, if it is chilly, wear a light jacket,else, if it is windy wear a windbreaker,else, if it is hot, wear no jacket.

Page 16: The if Statement

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if-else-if Statementsif (expression) statement or blockelse if (expression) statement or block // Put as many else ifs as needed here else statement or block Care must be used since else statements

match up with the immediately preceding unmatched if statement.

Page 17: The if Statement

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if-else-if Flowchart

Page 18: The if Statement

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Nested if Statements If an if statement appears inside of another if

statement (single or block) it is called a nested if statement.

The nested if is only executed if the if statement it is in results in a true condition.

Nested if statements can get very complex, very quickly.

Page 19: The if Statement

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Nested if Statement Flowcharts

Wear a jacket.

YesIs it coldoutside?

Wear shorts.Is it

snowing?

Wear a parka.

No

No Yes

Page 20: The if Statement

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if-else Matching Curly brace use is not required if there is only

one statement to be conditionally executed. However, sometimes curly braces can help

make the program more readable. Additionally, proper indentation makes it

much easier to match up else statements with their corresponding if statement.

Page 21: The if Statement

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if-else Matchingif (employed == 'y'){

if (recentGrad == 'y'){

System.out.println("You qualify for the special interest rate.");}else{

System.out.println("You must be a recent college graduate to qualify.");}

}else{

System.out.println("You must be employed to qualify.");

}

This elsematcheswith thisif.

This elsematcheswith thisif.


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