COMP 110CONDITIONALS

Instructor: Jason Carter

2

MORE ON CONDITIONALS

Miscellaneous (Side effects) Style issues Early returns

3

FOUR KINDS OF METHODS

public void setWeight (double newVal) { weight = newVal;}

public static double calculatBMI(double weight, double height) {

return weight/(height*height);}

public int getWeight() { return weight;}

public static int readNextNumber() { System.out.println(”Next Number:"); return Keyboard.readInt();}

procedure

functionpure function

setWeight(70);

calculateBMI(70, 1.77)

calculateBMI(70, 1.77)

…

24.57

24.57

getWeight() 70setWeight(77) getWeight() 77

impure function

getWeight() 77

541

readNextNumber ()

5readNextNumber ()

4

impure function with side effects

4

SIDE EFFECTS

public int getWeight() { System.out.println(“get Weight called” ); return weight; }

public static int readNextNumber() { System.out.println(”Next Number:"); return new Keyboard.readInt();}

public int increment() { counter++; return counter; }

Effect other than computing the return value

Printing something

Reading input

Changing global variable

5

ALTERNATIVE TO CHANGING A GLOBAL VARIABLE

public int increment() { counter++; return counter; }

public void incrementCounter() { counter++; }

public int getCounter() { return counter; }

6

IF-ELSE VS. BOOLEAN EXPRESSIONS

public static boolean hasFailed(int score) {if (score < PASS_CUTOFF)

return true;else

return false;}

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IF-ELSE STYLE

public static boolean hasFailed(int score) {return score < PASS_CUTOFF;

}

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IF-ELSE: REDUNDANT TEST

public static char toLetterGrade (int score) {if ((score >= A_CUTOFF == true)

return 'A';else if (score >= B_CUTOFF == true)

return 'B';else if (score >= C_CUTOFF == true)

return 'C';else if (score >= D_CUTOFF == true)

return 'D';else

return 'F';}

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NESTED IF-ELSE

public static char toLetterGrade (int score)if ((score >= A_CUTOFF)

return 'A';else if (score >= B_CUTOFF)

return 'B';else if (score >= C_CUTOFF)

return 'C';else if (score >= D_CUTOFF)

return 'D';else

return 'F';}

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ELSE BRANCHING

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THEN BRANCHING

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THEN BRANCHING

public static char toLetterGrade (int score)if (score >= D_CUTOFF)

if (score >= C_CUTOFF)if (score >= B_CUTOFF)

if (score >= A_CUTOFF)return 'A‘;

elsereturn 'B';

else // score < B_CUTOFFreturn 'C‘;

else // score < C_CUTOFFreturn 'D';

else // score < D_CUTOFFreturn 'F';

}

}

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BALANCED BRANCHING

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BALANCED BRANCHING

public static char toLetterGrade (int score) {if (score >= B_CUTOFF)

if (score >= A_CUTOFF) return 'A'; else

return 'B';else // score < B_CUTOFF

if (score < C_CUTOFF)if (score < D_CUTOFF)

return 'F';else

return 'D'; else // score >= C_CUTOFF

return 'C';}

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NESTED IF-ELSE STYLE

Linear branching preferable to balanced branches

Else branching preferable to then branching

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NO NESTING

public static char toLetterGrade (int score) {char result;if (score >= A_CUTOFF)

result = 'A';if ((score < A_CUTOFF) && (score >= B_CUTOFF))

result = 'B';if ((score < B_CUTOFF) && (score >= C_CUTOFF))

result = 'C';if ((score < C_CUTOFF) && (score >= D_CUTOFF))

result = 'D';if (score < D_CUTOFF)

result = F';return result;

}

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WHEN ELSE BRANCH IS NEEDED

public static char toLetterGrade (int score) {char result;if (score >= A_CUTOFF)

result = 'A';else if (score >= B_CUTOFF)

result = 'B';else if (score >= C_CUTOFF)

result = 'C';else if (score >= D_CUTOFF)

result = 'D';else

result = F';return result;

}

18

NO NESTING WITH EARLY RETURNS

public static char toLetterGrade (int score) {char result;if (score >= A_CUTOFF)

return 'A';else if (score >= B_CUTOFF)

return 'B';else if (score >= C_CUTOFF)

return 'C';else if (score >= D_CUTOFF)

return 'D';return F';

}

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EQUIVALENT SOLUTION

public static char toLetterGrade (int score) {if (score >= A_CUTOFF)

return 'A';else if (score >= B_CUTOFF)

return 'B';else if (score >= C_CUTOFF)

return 'C';else if (score >= D_CUTOFF)

return 'D';else

return F';}

20

EARLY RETURNS IN PROCEDURES

public void printLetterGrade(int score) { if (score < 0) {

System.out.println ("Illegal score");return;

} System.out.println(“Letter Grade:” + toLetterGrade(score”));

}

21

WITHOUT EARLY RETURN IN PROCEDURES

public void printLetterGrade(int score) { if (score < 0)

System.out.println ("Illegal score");else

System.out.println ("Letter Grade: ” + toLetterGrade(score));

}

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DANGLING ELSE

if (score >= B_CUTOFF)if (score >= A_CUTOFF)

System.out.println ("excellent!");else

System.out.println ("bad");}

Matching if?

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DANGLING ELSE: MATCHING OUTERMOST IF

if (score >= B_CUTOFF)if (score >= A_CUTOFF)

System.out.println ("excellent!");else

System.out.println ("bad");

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DANGLING ELSE: MATCHING INNERMOST IF

if (score >= B_CUTOFF)if (score >= A_CUTOFF)

System.out.println ("excellent!");else

System.out.println ("bad");

Correct interpretation

25

NESTED IF-ELSE STYLE REMINDER

Linear Branching preferable to Balanced Branches

Else Branching Preferable to Then Branching Do not have dangling-else ambiguity