teaching machines

CS 145 Lecture 12 – Conditionals and file input

October 21, 2011 by Chris Johnson. Filed under cs145, fall 2011, lectures.

Agenda

• generating an ordinal number
• if/else if
• reading from files (brief treatise on exceptions)
• test-driven development
• categorizing light

Code

Ordinals.java

package lecture;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class Ordinals {
  public static void main(String[] args) throws FileNotFoundException {
    Scanner in = new Scanner(new File("/home/cjohnson/Desktop/ordinals.txt"));

    while (in.hasNextInt()) {
      int i = in.nextInt();
      String expected = in.next();
      String actual = getOrdinal(i);
      if (!actual.equals(expected)) {
        System.out.println("Expected: " + expected + " but Actual: " + actual);
      }
    }

    in.close();
  }

  public static String getOrdinal(int n) {
    
    int positiveN = Math.abs(n);
    
    if (positiveN % 100 >= 11 && positiveN % 100 <= 13) { // All numbers with 11,12,13 in units/tens places
      return n + "th";
    } else if (positiveN % 10 == 1) { // All numbers with 1 in units place
      return n + "st";
    } else if (positiveN % 10 == 2) { // All numbers with 2 in units place
      return n + "nd";
    } else if (positiveN % 10 == 3) {
      return n + "rd";
    } else {
      return n + "th";
    }
  }
}

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