teaching machines

CS1: Lecture 20 – If Bifurcations

Dear students,

The software we can now write feels alive. We can get user input. We can ask questions about it. And we can respond in different ways with conditional statements. These conditional statements appear in three general forms. Last time we saw the diversion form, in which we perform some extra work when a condition is true. Today we visit another pattern: the bifurcation.

Bifurcations

In a bifurcation, we use a boolean criteria to choose between two mutually exclusive actions. Let’s write some programs that demonstrate this pattern.

  • Flashmod—which prompts the user to solve a mod problem
  • Sometimes—which presents a web page that is sometimes red and sometimes blue
  • Whichwise—at the Ade Olson track, you must run clockwise on even days
  • Birthday—is today the day?

TODO

Here’s your TODO list to complete before we meet again:

  • Keep at homework 3. Remember to commit and push after every coding session!
  • The Chippewa Valley Code Camp is on Saturday, October 26, at CVTC. A bunch of local software developers will be speaking on a variety of technologies and industry practices. Food is provided. Attend, write up a quarter sheet documenting what you learn, and turn it in on Monday, October 28, for an extra credit participation point.

See you next class!

Sincerely,

P.S. It’s time for a haiku!

Computers don’t think
You know what AI stands for?
A whole lotta Ifs

P.P.S. Here’s the code we wrote together in class…

FlashMod.java

package lecture1018.cs145;

import java.util.Random;
import java.util.Scanner;

public class FlashMod {
  public static void main(String[] args) {
    Random generator = new Random();
    int a = generator.nextInt(101);
    int b = generator.nextInt(10) + 1;
    int answer = a % b;

    System.out.printf("%d %% %d = ", a, b);

    Scanner in = new Scanner(System.in);
    int guess = in.nextInt();

    if (guess == answer) {
      System.out.println("You got it!");
    } else {
      System.out.println("\uD83D\uDCA9");
    }
  }
}

SometimesRedSometimesBlue.java

package lecture1018.cs145;

import java.util.Random;

public class SometimesRedSometimesBlue {
  public static void main(String[] args) {
    Random generator = new Random();
    String color;
    if (generator.nextBoolean()) {
      color = "blue";
    } else {
      color = "red";
    }
    String html = String.format("<html><head><title>Red || Blue</title></head><body style=\"background-color: %s;\"></body></html>", color);
    System.out.println(html);
  }
}

Whichwise.java

package lecture1018.cs145;

import java.util.Calendar;
import java.util.GregorianCalendar;

public class Whichwise {
  public static void main(String[] args) {
    GregorianCalendar now = new GregorianCalendar();
    int day = now.get(Calendar.DAY_OF_MONTH);
    if (day % 2 == 0) {
      System.out.println("\uD83D\uDD03");
    } else {
      System.out.println("\uD83D\uDD04");
    }
  }
}

FlashMod.java

package lecture1018.cs148;

import java.util.Random;
import java.util.Scanner;

public class FlashMod {
  public static void main(String[] args) {
//    double foo = 5 / 0.0;
//    System.out.println(foo + Math.PI);
    Random generator = new Random();
    int random1 = 30 + generator.nextInt(70);
    int random2 = 1 + generator.nextInt(30);
    int answer = random1 % random2;
    System.out.printf("%d %% %d = ", random1, random2);

    Scanner in = new Scanner(System.in);
    int guess = in.nextInt();

    if (guess == answer) {
      System.out.println("\uD83E\uDD20");
    } else {
      System.out.println("\uD83D\uDE02");
    }
  }
}

Sometimes.java

package lecture1018.cs148;

import java.util.Random;

public class Sometimes {
  public static void main(String[] args) {

    Random generator = new Random();
    String color;
    if (generator.nextBoolean()) {
      color = "blue";
    } else {
      color = "gold";
    }

    String html = String.format("<html><head><title>Blu || Gold</title></head><body style=\"background-color: %s;\"></body></html>", color);
    System.out.println(html);
  }
}

Whichwise.java

package lecture1018.cs148;

import java.util.Calendar;
import java.util.GregorianCalendar;

public class Whichwise {
  public static void main(String[] args) {
    GregorianCalendar now = new GregorianCalendar();
    int day = now.get(Calendar.DAY_OF_MONTH);

    if (day % 2 == 1) {
      System.out.println("\u27f3");
    } else {
      System.out.println("\u27f2");
    }
  }
}

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