teaching machines

CS 145 Lecture 6

September 26, 2011 by Chris Johnson. Filed under cs145, fall 2011, lectures.

Topics Covered

• what does this do?
• facing off the computer in guess-a-number
• generating a random spelunking workout
• an acrostic editor
• calculating average cell phone payment

What does this do?

1. public static String ?(??) {
    return text + " :)";
   }

2. public static ? ??(String text) {
     return text.length() == 0;
   }

3. public static ? ??(String text) {
     int index = text.indexOf('.');
     return text.substring(0, index + 1);
   }

Code

GeometryFun.java

package lecture;

import java.util.Scanner;


public class GeometryFun {
  public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    System.out.print("Enter radius: ");
    double value = in.nextDouble();
    double area = getAreaOfCircle(value);
    System.out.println("Area: " + area);
    
//    getAreaOfCircle("t");
    
    System.out.println(getAreaOfAnnulus(6, 8));
  }
  
  public static double getAreaOfCircle(double radius) {
    double area = radius * radius * Math.PI;
//    radius = 6.0; // this has absolutely no effect on anything at all
    return area;
  }
  
  // meaningful name?
  // return type?
  // outside information?
  
  public static double getAreaOfAnnulus(double insideRadius, double outsideRadius) {
    double insideArea = getAreaOfCircle(insideRadius);
    double outsideArea = getAreaOfCircle(outsideRadius);
    double totalArea = outsideArea - insideArea;
    return totalArea;
  }
  
  public static double f(double t) {
    return 1 / (1 + Math.sqrt(t));
  }
//  
  public static double getEdgeOfCube(double diagonalLength) {
    // find diagonal of bottom face
    double edgeLength = diagonalLength / Math.sqrt(3);
    return edgeLength;
  }
  
  
  
  
  
  
  
  
  
  
  
  
}

GuessANumber.java

package lecture;

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

public class GuessANumber {
  public static void main(String[] args) {
    // think of a number
    
    // computer generate a #
    // see if #s same
    // respond to correctness
    
    // computer generate a #
    // see if #s same
    // respond to correctness
    
    Random generator = new Random();
    boolean isSame = false;
    
    Scanner in = new Scanner(System.in);
    System.out.print("Your number in [0, 5]: ");
    int answer = in.nextInt();
    
    while (isSame == false) {
      int guess = generator.nextInt(6); // number between 0 and 5
      isSame = (answer == guess);
      System.out.println("The computer's answer (" + guess + ") is right? " + isSame);
    }
  }
}

SpelunkingFitnessDisplay.java

package lecture;

import java.util.Random;

public class SpelunkingFitnessDisplay {

  public static void main(String[] args) {
    
    printLine();
  }
  
  public static void printLine() {
    
    Random generator = new Random();
    int nDots = generator.nextInt(11);
    System.out.println(nDots);
    
    while (nDots > 0) {
      System.out.print("*");
      nDots = nDots - 1;
    }
  }
}

TODO

• Read sections 3.1 through 3.3.

Haiku