Darrell Bethea May 19, 2011 1 Assignments: Homework 0 grades up - - PowerPoint PPT Presentation

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Darrell Bethea May 19, 2011 1 Assignments: Homework 0 grades up - - PowerPoint PPT Presentation

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Darrell Bethea May 19, 2011 1 Assignments: Homework 0 grades up Program 1 due yesterday Program 2 due Monday Program 3 assigned today Updated yesterdays slides 2 3 Loops Body Initializing Statements

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Darrell Bethea May 19, 2011

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 Assignments:

  • Homework 0 grades up
  • Program 1 due yesterday
  • Program 2 due Monday
  • Program 3 assigned today

 Updated yesterday’s slides

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 Loops

  • Body
  • Initializing Statements
  • Ending a loop
  • Bugs

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count = 1; while (count <= num) { System.out.print(count + “, “); count++; }

 Repeated code  Write pseudocode and turn repeated

statements into loops

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 Get user input  sum = sum + input  Get user input  sum = sum + input  Get user input  sum = sum + input  Average sum

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Repeated statements in pseudocode become your loop

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 Get user input  sum = sum + input

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sum = sum + input

 Variables in your loop must be initialized (set

to a value) before the loop

 What is initialization of sum?

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sum = sum + input

 Variables in your loop must be initialized (set

to a value) before the loop

 What is initialization of sum?

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 What if we wanted the product?

  • sum = sum * input
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 If you know number of loop iterations?

 Count-controlled loops  for(count = 0; count < iterations; count++)

 User controlled ending

 Ask-before-iterating  Sentinel value

 Booleans

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for (count = 0; count < iterations; count++) { System.out.print(“I have iterated”); System.out.println((count + 1) + “ times”); }

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do { //do stufg in your code here System.out.print( “Continue? yes/no”); answer = keyboard.next(); } while (answer.equalsIgnoreCase(“yes”));

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 Signal end of input System.out.print(“enter a negative number to end the loop”); next = keyboard.nextInt(); sum = 0; while ( next >= 0 ) {

  • sum = sum + next;
  • System.out.print(“Enter a number: ”);
  • next = keyboard.nextInt();

}

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int next, sum = 0; boolean numbersLeft = true; Scanner keyboard = new Scanner(System.in); while (numbersLeft) { next = keyboard.nextInt(); if (next < 0) { numbersLeft = false; } else { sum = sum + next; } } System.out.print(“the sum is “ + sum);

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13 Output: Value of count: Value of count2:

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2:

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2:

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2:

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2:

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2: 1

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2: 1

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2: 1

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2: 1

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2: 1

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2: 1 1

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2: 1 1

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2: 2 1

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2: 2 1

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2: 2

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2: 2

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2: 2

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2: 2 1

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: Value of count: Value of count2: 2 1

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 Value of count: Value of count2: 2 1

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 Value of count: Value of count2: 2 2

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 Value of count: Value of count2: 2 2

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 Value of count: Value of count2: 3 2

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 Value of count: Value of count2: 3 2

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 Value of count: Value of count2: 3

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 Value of count: Value of count2: 3

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 Value of count: Value of count2: 3

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 Value of count: Value of count2: 3 1

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 Value of count: Value of count2: 3 1

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 1 Value of count: Value of count2: 3 1

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 1 Value of count: Value of count2: 3 2

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 1 Value of count: Value of count2: 3 2

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 2 1 Value of count: Value of count2: 3 2

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 2 1 Value of count: Value of count2: 3 3

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 2 1 Value of count: Value of count2: 3 3

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 2 1 Value of count: Value of count2: 3 4

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 2 1 Value of count: Value of count2: 3 4

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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13 Output: 1 2 1 Value of count: Value of count2: 3 4

int count, count2; for (count = 0; count <= 3; count++) { for (count2 = 0; count2 < count; count2++) { System.out.println(count2); } }

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 Give a Java loop statement that will set the

variable result equal to 25.

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 Problem with program preventing correct

execution

 Two most common mistake in loops

  • Ofg-by-one errors
  • Infinite Loops!!!!!!

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 Loop repeats one too many or one too few

times

 for (count = 1; count < 10; count++);

  • Loop 9 times

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 A loop which repeats without ever ending

is called an infinite loop.

 If the controlling boolean expression

never becomes false, a loop will repeat without ending.

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count = 1; while (count <= num) { System.out.print(count + “, “); //count++; }

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count = 1; while (count <= num); { System.out.print(count + “, “); count++; }

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int count;

// initializing action; boolean expression; update action

for (count = 1; count >= num; count++) { System.out.print(count + “, “); }

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 Error checking

  • System.out.print(variable);
  • Run on simple input

 Debugger

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