CS1101: Programming Methodology Recitation 3 – Control Structures

CS1101: Programming MethodologyRecitation 3 – Control Structures

Checksum Validation • Objective: Develop a program that validates a Universal Product Code (UPC) number. • A valid UPC is a 12 digit value that meets the criteria: • m is the sum of 2nd, 4th, 6th, 8th, 10th digits • n is the sum of the 1st, 3rd, 5th, 7th, 9th, 11th digits • r = 10 – ((m + 3.n) mod 10) • Valid UPC number if 12th digit is equal to r

Checksum Validation • Example: 780070121354 • m = 8 + 0 + 0 + 2 + 3 = 13 • n = 7 + 0 + 7 + 1 + 1 + 5 = 21 • r = 10 – ((13 + 3.21) mod 10) • = 10 – (76 mod 10) = 10 – 6 = 4 • Example: 123456789011 • m = 2 + 4 + 6 + 8 + 0 = 20 • n = 1 + 3 + 5 +7 + 9 + 1 = 26 • r = 10 – ((20 + 3.26) mod 10) • = 10 – (98 mod 10) = 10 – 8 = 2

Analysis and Design: • Values m, n and r • Input string s and its numeric representation number • With number, the 12 component digits d1, d2 …, d12 can be determined for initializing m, n and r

Analysis and Design: • Prompt user to supply 12 digit number • Extract input and assign to s • Convert s to a numeric representation number. • If number is negative or has more than 12 digits Then report number is not a UPC code Else Assign least significant (12th) digit of number to d12 Assign 11th digit of number to d11 : Assign 1st digit of number to d1 Compute m = d2+d4+d6+d8+10 Compute n = d1+d3+d5+d7+d9+d11 Compute r = 10 – ((m – 3.n) mod 10) If r = d12 Then report number is a feasible UPC code Else report number is not a UPC code

// Checks whether a user-specified value meets the UPC criteria import java.io.*; public class UPC { // main(): application entry point public static void main(String[] args) throws IOException { final long MAX_POSSIBLE_UPC_CODE = 999999999999L; // set input stream and get number BufferedReader stdin = new BufferedReader( new InputStreamReader(System.in)); System.out.print("Enter a 12-digit whole number: "); String s = stdin.readLine(); long number = Long.parseLong(s); max int value is only 10 digits. Use long to represent UPC code

// determine whether number is a possible upc code if ((number < 0) || (number > MAX_POSSIBLE_UPC_CODE)) { // not a upc code System.out.println(s + " is an invalid UPC code"); } else { // might be a upc code, determine individual digits int d12 = (int) (number % 10); number /= 10; int d11 = (int) (number % 10); number /= 10; int d10 = (int) (number % 10); number /= 10; int d9 = (int) (number % 10); number /= 10; int d8 = (int) (number % 10); number /= 10; int d7 = (int) (number % 10); number /= 10; int d6 = (int) (number % 10); number /= 10; int d5 = (int) (number % 10); number /= 10; int d4 = (int) (number % 10); number /= 10; int d3 = (int) (number % 10); number /= 10; int d2 = (int) (number % 10); number /= 10; int d1 = (int) (number % 10); number /= 10; % - Java modulus operator

// compute sums of first 5 even digits and the odd digits int m = d2 + d4 + d6 + d8 + d10; int n = d1 + d3 + d5 + d7 + d9 + d11; // use UPC formula to determine required value for d12 int r = 10 - ((m + 3*n) % 10); // based on r, can test whether number is a UPC code if (r == d12) { // is a upc code System.out.println(s + " is a feasible UPC code"); } else { // not a upc code System.out.println(s + " is an invalid UPC code"); } } } }

Nested if statements Print three messages depending on test score and student age if (testScore >= 70) { if (studentAge < 10) System.out.println (“You did a great job!”); else System.out.println (“You did pass”); //test score >= 70 and age >=10 } else System.out.println (“You did not pass”); //test score < 70 if (testScore >= 70 && studentAge < 10) { System.out.println (“You did a great job!”); } else { //either test score < 70 OR age >=10 if (testScore >= 70) System.out.println (“You did pass”); else System.out.println (“You did not pass”); }

Nested if statements Input 3 integers and determine how many of them are negative if (num1 < 0) { if (num2 < 0) { if (num3 < 0) negativeCount = 3; //all three are negative else negativeCount = 2; //num1 and num2 are negative } else { if (num3 < 0) negativeCount = 2; // num1 and num3 are negative else negativeCount = 1; // num1 is negative } } else { if (num2 < 0) { if (num3 < 0) negativeCount = 2; // num2 and num3 are negative else negativeCount = 1; // num2 is negative } else { if (num3 < 0) negativeCount = 1; // num3 is negative else negativeCount = 0; // no negative numbers } }

Nested if statements Input 3 integers and determine how many of them are negative More elegant version! negativeCount = 0; if (num1 < 0) negativeCount ++; if (num2 < 0) negativeCount ++; if (num3 < 0) negativeCount ++;

Rules for if statements • Minimize number of nestings • Avoid complex boolean expressions. • - Make them as simple as possible. • - Don’t include many ANDs and ORs. • Eliminate unnecessary comparisons. • Don’t be satisfied with first correct statement. • Always look for improvement • 5. Read your code again. • Can you follow the statement easily ? • If not, try to improve it.

Dataset Analysis • Objective: Develop a program that finds the min, max, and mean of a dataset of values. • Analysis and Design: • Methods: • public double getMinimum() • public double getMaximum() • public doublegetAverage() • These methods return double.NaN if dataset is empty

Dataset Analysis • Analysis and Design: • Constructors: • public DataSet () – initialize representation of an empty dataset • Public DataSet (String s) – initialize dataset with values from file with name s • 3. member methods – getSize(), addValue (double x), • clear(), load (String s) • Instance variables: • private int n • private double minimumValue • private double maximumValue • private double xSum

import java.io.*; public class DataSetTester { public static void main(String[] args) throws IOException { DataSet dataset = new DataSet("age.txt"); System.out.println(); System.out.println("Minimum: " + dataset.getMinimum()); System.out.println("Maximum: " + dataset.getMaximum()); System.out.println("Mean: " + dataset.getAverage()); System.out.println("Size: " + dataset.getSize()); System.out.println(); dataset.clear(); dataset.load("stature.txt"); System.out.println("Minimum: " + dataset.getMinimum()); System.out.println("Maximum: " + dataset.getMaximum()); System.out.println("Mean: " + dataset.getAverage()); System.out.println("Size: " + dataset.getSize()); System.out.println(); } }

// Data set summary representation import java.io.*; public class DataSet { // instance variables private int n; private double xSum; private double minimumValue; private double maximumValue; // DataSet(): default constructor public DataSet() { clear(); } // DataSet(): specific constructor public DataSet(String s) throws IOException { load(s); }

// clear(): empties the data set public void clear() { n = 0; xSum = 0; minimumValue = Double.NaN; maximumValue = Double.NaN; } // add(): adds the value to the set public void addValue(double x) { xSum += x; ++n; if (n == 1) { minimumValue = maximumValue = x; } else if (x < minimumValue) { minimumValue = x; } else if (x > maximumValue) { maximumValue = x; } }

// load(): adds the values from the file to set public void load(String s) throws IOException { // get a reader for the file BufferedReader fileIn = new BufferedReader( new FileReader(s)); // add values one by one String currentLine = fileIn.readLine(); while (currentLine != null) { double x = Double.parseDouble(currentLine); addValue(x); currentLine = fileIn.readLine(); } // close up file fileIn.close(); }

// getAverage(): compute data set average public double getAverage() { if (n == 0) return Double.NaN; else return xSum / n; } // getMinimum(): produce minimum data set value public double getMinimum() { return minimumValue; } // maximum(): produce maximum data set value public double getMaximum() { return maximumValue; } // getSize(): produce data set size public int getSize() { return n; } }

CS1101: Programming Methodology Recitation 3 – Control Structures