INFO Problem Solving and Programming Logic INFO Problem Solving and Programming Logic Arrays Sorting

9/20/2015Wendi Jollymore, ACES2 Array Concepts Index data n - 2 n - 1 Array Element length = n

9/20/2015Wendi Jollymore, ACES3 Array Concepts Why do we use them? See example in notes

9/20/2015Wendi Jollymore, ACES4 Coding Arrays Define the type and length Pseudocode: integer arrayName[n] Assumes 0-based array First index is 0, last index is n-1 Java: int[] arrayName = new int[n];

9/20/2015Wendi Jollymore, ACES5 Coding Arrays Accessing elements: Pseudocode: Print numbers[i] firstNames[i] = “Fred” Java: System.out.println(numbers[i]); firstNames[i] = “Fred”;

9/20/2015Wendi Jollymore, ACES6 Coding Arrays Fill an array with values: Print and calculate average: integer numbers[10] For counter = 0 to 9 Print "Enter number ", counter+1 Get numbers[counter] For counter = 0 to 9 Print numbers[counter] Add numbers[counter] to total Print total / 10

9/20/2015Wendi Jollymore, ACES7 Exercises Try the three exercises in the notes: A string array called names[] with 25 elements contains the last names of all the salespeople in a company. Write the pseudocode to ask the user for a salesperson's name, then sequentially search the array for that person's name. For all matches in the list, display the index number. Otherwise, display a "not found" message.

9/20/2015Wendi Jollymore, ACES8 Exercises Rewrite the pseudocode at the beginning of this lesson using an array for the grades, but record grades for 6 courses. Ask the user to enter five numbers. Store the numbers in an array and then determine if the numbers were entered in ascending order. Display a message indicating whether they are sorted or not.

9/20/2015Wendi Jollymore, ACES9 Parallel Arrays For grades example What if we wanted to display course code? See code in notes PROG10082 INFO16029 MATH26507 SYST16529 SYST String[] coursesfloat[] grades index

9/20/2015Wendi Jollymore, ACES10 Exercise A program calculates the total revenue for various items sold in a kiosk. There are 2 arrays: price[] and quantity[]. The price[] array contains the prices of 25 items, and the quantity[] array contains the quantity[] of each of the 25 items sold. For example, price[3] contains the price of item 4 and quantity[3] contains the number of item 4's sold. Create a third array, revenue[] that is parallel to price[] and quantity[]. Fill this array with the total revenue of each of the 25 items. Revenue = price * quantity sold.

9/20/2015Wendi Jollymore, ACES11 Sorting Arrays Many different sort algorithms Choice depends on size of list Bubble Sort Simplest, easiest to learn Good for small lists (n <= 28) Demo…

9/20/2015Wendi Jollymore, ACES12 Sorting Arrays Bubble Sort summary: Number of passes: n – 1 Each pass puts one more element in its correct position Each pass has x – 1 comparisons Let x = # of unsorted elements Maximum number of comparisons: The sum of the values from 1 to n-1 n-1 ∑ i i=1

9/20/2015Wendi Jollymore, ACES13 Exercises Sort these in ascending order: Try sorting in descending order For an array with 6 elements: How many passes? How many comparisons in total? For an array with 7 elements?

9/20/2015Wendi Jollymore, ACES14 Bubble Sort Logic Explained in the notes The main action taking place is swapping E.g. if a pair of items are out of order, swap! If grades[currEl] > grades[currEl+ 1] Then tempGrade = grades[currEl] grades[currEl] = grades[currEl + 1] grades[currEl + 1] = tempGrade End If

9/20/2015Wendi Jollymore, ACES15 Bubble Sort Logic One Pass: numComparisons = numberElements - 1 currEl= 0 While currEl < numComparisons If grades[currEl] > grades[currEl + 1] Then tempGrade = grades[currEl] grades[currEl] = grades[currEl + 1] grades[currEl + 1] = tempGrade End If Add 1 to currEl

Bubble Sort Logic All Passes: 9/20/2015Wendi Jollymore, ACES16 passNumber = 1 numComparisons = numberElements - 1 While passNumber <= numberElements – 1 currEl= 0 While currEl < numComparisons If grades[currEl] > grades[currEl + 1] Then tempGrade = grades[currEl] grades[currEl] = grades[currEl + 1] grades[currEl + 1] = tempGrade End If Add 1 to currEl Subtract 1 from numComparisons Add 1 to passNumber

Other Sort Algorithms Sorting is usually part of a larger course in Data Structures See links in notes for more sort algorithms 9/20/2015Wendi Jollymore, ACES17