8:00 Quiz 1

Statistics:

mean     21.688 (347.000/16)
stddev   4.984
median   22.000
midrange 20.000-25.000

# avg
1 6.94 / 10
2 8.44 / 10
3 6.31 / 10

Question 1-1

Suppose a user executes the following run() method and types the numbers 3.

public static void run() {
    int n = IO.readInt();
    int i = 0;
    while(n != 1) {
        if(n % 2 == 1) n = 3 * n + 1;
        if(n % 2 == 0) n /= 2;
        i++;
    }
    IO.println(i);
}

Show all the values taken on by the variables of the program.

n
i

What does the method print?

Question 1-2

Say we execute the following method.

import csbsju.cs160.*;

public class Q1A {
  public static void run() {
    DrawableFrame w;
    w = new DrawableFrame();
    w.show();
    Graphics g = w.getGraphics();
    g.fillRect(50, 50, 100, 100);
    g.setColor(Color.white);
    g.fillRect(75, 0, 50, 200);
    g.fillRect(0, 75, 200, 50);
  }
}

The fillRect() method draws a filled rectangle. It takes four integer parameters: the left side's x-coordinate, the top side's y-coordinate, the width, and the height.

Complete the below window as it will appear on the screen.

Question 1-3

Fill in run() so that, when executed, the method will count the number of positive numbers the user types before the user types 0. A user executing the method should see the following, for example. (Boldface indicates what the user types.)

In this case, the program displays 3, because the user typed three positive numbers (123, 8, and 123).

import csbsju.cs160.*;
public class CountPositives {
    public static void run() {



    }
}

Solutions

Solution 1-1

n   3    10  5    16  8     4     2     1
i      0        1        2     3     4     5

It prints ``5.''

Solution 1-2

Solution 1-3

import csbsju.cs160.*;
public class CountPositives {
    public static void run() {
        int count = 0;
        while(true) {
            int n = IO.readInt();
            if(n == 0) break;
            if(n > 0) ++count;
        }
        IO.println(count);
    }
}