Questions

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Concept - Loop algorithms

There are certain sets of code containing loops that we use over and over (algorithms)

• Finding sum and average
• Maximum and minimum
• Counting matches
• Finding the first match
• Prompting until a correct value is entered

 

Concept - Finding sum and average

That is what you did last time with Lesson 12 Q6.

• The problem:

  Write a program to ask the user for input to represent the result of the throw. Find the sum of the numbers and then the average. Use Q as a sentinel value.

• The code:

  import java.util.Scanner;
  public class InputTest
  {
      public static void main(String[] args)
      {
          Scanner scan = new Scanner(System.in);
          double value = 0;
          double sum = 0;
          int count = 0;
          
          System.out.print("Enter a number. Q to quit: ");
          while (scan.hasNextDouble())
          {
              value = scan.nextDouble();
              sum = sum + value;
              count++;
              System.out.print("Enter a number another number. Q to quit: ");
          }
          
          System.out.println("Sum: " + sum);
          double average = 0;
  
          if (count > 0)
          {
              average = sum / count;
          }
          System.out.println("Average: " + average);
      }
  }
    

Activity - Find average

Record your participation in Piazza clicker question Lesson13 Q1

Write a program to get the height of students from the user as a double and find the average height of all the students in a group.

You can use input_practice.zip from last lesson to save time

1. I got it, no real problem
2. I got it, but it was hard
3. I couldn't do it in the time allowed
4. I didn't know where to start

 

Concept - Finding the maximum

Let's visually find the tallest in a group of students.

 

Activity - Find the shortest

Record your participation in Piazza clicker question Lesson13 Q2

On a piece of paper or in a text editor, write simple pseudocode to find the shortest student in a set of students. Just write the algorithm. Don't worry about input or output

 

Activity - Translate pseudocode to Java code

Record your participation in Piazza clicker question Lesson13 Q3

Using this pseudocode for finding the minimum, write a program to get a set of heights from the user. Terminate when a non-number is entered. Then print the minimum height (the shortest). You can use input_practice.zip.

Declare a variable to hold the minimum
Prompt the user to enter a height
minimum = nextDouble()
Prompt the user to enter a height or q to quit
While another double has been entered
  read a value for height
  if the height is less than the current minimum
      Set the value of minimum to  height
   Prompt again
Print the minimum

1. I got it, no real problem
2. I got it, but it was hard
3. I couldn't do it in the time allowed
4. I didn't know where to start

Concept - Problems with this implementation

• What if the user enters a non-double as the first value?
• We have to prompt 3 times
• We will see later how to solve these problems

 

Concept - Counting Matches

Let's visually count the number of students 5.5 feet tall or taller.

 

Activity - Count matches

Record your participation in Piazza clicker question Lesson13 Q4

Write the pseudocode of an algorithm to determine how many students are 5.5 feet tall or taller.

 

Activity - Count matches

Record your participation in Piazza clicker question Lesson13 Q5

Write a program to determine how many students are 5.5 feet tall or taller. Starter code is in count_matches_project. It does the input for you. You need to add the counting matches algorithm code.

1. I got it, no real problem
2. I got it, but it was hard
3. I couldn't do it in the time allowed
4. I didn't know where to start

 

Activity - Infinite loop

Record your participation in Piazza clicker question Lesson13 Q6

How would you write a loop that will not terminate. That means the condition will alwas be true.

• You can kill the program by right clicking on the arrow in the lower righ tcorner and selecting "Reset Virtual Machine"

Concept: finding the first match

Find the position of the first space in a string using a loop

• We may not need to look at all characters so we will use a while loop.
• The search can terminate in two ways
  • we find what we are looking for
  • we get to the end of the string
• The algorithm:

  boolean found = false;
  String ch = "?";
  int position = 0;
  while (!found && position < str.length())
  {
     ch = str.substring(position, position + 1);
     if (ch.equals(" ")) 
     { 
         found = true; 
     }
     else 
     { 
         position++; 
     }
  }

Activity - Finding the first match

Record your participation in Piazza clicker question Lesson13 Q7

Write a program to ask the user for a string (use nextLine()). Then find and print the position of the first @. Here is another link to input_practice.zip We are practicing loops so use a loop.

1. I got it, no real problem
2. I got it, but it was hard
3. I couldn't do it in the time allowed
4. I didn't know where to start