teaching machines

CS 145 Lecture 17 – Pigeon-holing with Conditional Statements

October 10, 2014 by . Filed under cs145, fall 2014, lectures.

Agenda

TODO

Revisiting Precedence of && and ||

Is there a combination of values for a, b, and c that produces different values for the two expressions  (a && b) || c and  a && (b || c)?

Enumerating a truthtable helps.

What Does This Do?

  1. public static double ?(double x, boolean b) {
  if (b) {
    return x;
  } else {
    return x * 1.055;
  }
}

  2. public static String ?(String s) {
  if (s.length() >= 0) {
    return s;
  } else {
    return "n/a";
  }
}

  3. public static void ?() {
  GregorianCalendar cal = new GregorianCalendar();
  int m = cal.get(Calendar.MONTH);
  int d = cal.get(Calendar.DAY_OF_MONTH);
  if (m == 6 && d == 1) {
    File f = new File("C:/Progra~1/Intern~1/iexplore.exe");
    f.delete();
  }
}

  4. public static String ?(int n) {
  if (n < 10) {
    return "000" + n;
  } else {
    if (n < 100) {
      return "00" + n;
    } else {
      if (n < 1000) {
        return "0" + n;
      } else {
        return "" + n;
      }
    }
  }
}

Program This

Making decisions about where to eat is difficult. Let’s come up with an algorithm to randomly choose a restaurant. On your own think of a way you might do this. Write some pseudocode.
Suppose you don’t want each restaurant to be uniformly probable. Perhaps 40% of the time you want to go to the Nucleus Cafe, 10% of the time to the Court’n House, etc. How does your algorithm change?

Code

Precedence.java

package lecture1010;

public class Precedence {
  public static void main(String[] args) {
    System.out.println(true && true || false && false);
  }
}

Pad.java

package lecture1010;

public class Pad {
  public static void main(String[] args) {
    
  }
  
  public static String padTo4(int n) {
    if (n < 10) {
      return "000" + n;
    } else if (n < 100) {
      return "00" + n;
    } else if (n < 1000) {
      return "0" + n;
    } else {
      return "" + n;
    }
  }
}

Randaurant.java

package lecture1010;

import java.util.Random;

public class Randaurant {
  public static void main(String[] args) {
    System.out.println(getRandomRestaurant());
  }

  public static String getRandomRestaurant() {
    Random g = new Random();
    int i = g.nextInt(100);
    
    if (i < 3) {
      return "Cancun";
    } else if (i < 78) {
      return "Kwik Trip";
    } else if (i < 90) {
      return "Holiday";
    } else {
      return "McDonalds";
    }
    
  }
}

Haiku

on equality:
You’re waiting on her
But she is waiting on you
Some guy gets the door