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Subgoals

Section 7.6 Worked Example: While Loops - Sentinel

Subgoals for Evaluating a Loop.

  1. Identify loop parts
    1. Determine start condition
    2. Determine update condition
    3. Determine termination condition
    4. Determine body that is repeated
  2. Trace the loop
    1. For every iteration of loop, write down values

Subsection 7.6.1

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Problem: The following code counts the number of valid values that are entered and stops when an invalid input is entered. What is the output if the user enters the values: 10, 15, 20, 25, 30, 35, -1?
System.out.println("Enter a negative score to signal the end of input.");
int gdScores = 0;
int score;
System.out.print("Score: ");
Scanner get = new Scanner(System.in);
score = get.nextInt();
while (score >= 0)
{
     if (score >= 20)
         gdScores++;
     System.out.print("Score: ");
     score = get.nextInt();
 }
System.out.println("Number of good scores: " + gdScores);

Subsection 7.6.2 SG1: Diagram which statements go together.

Figure 7.6.1.

Subsection 7.6.3 SG2: Define and initialize variables

Start:
score = 10;
End:
score < 0
Figure 7.6.2.

Subsection 7.6.4 SG3: Trace the loop

Figure 7.6.3.
Answer.
Number of good scores: 4

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