Review for Midterm 0

Question 0-1

Write a program to print a triangle of asterisks as in the third problem of Lab 0.

Width? 5
*****
****
***
**
*

To accomplish this, define two static methods. The first takes a parameter num and prints a line containing num asterisks. And the main() method should use this method to accomplish the overall task.

import csbsju.cs160.*;

public class PrintTriangle {
    public static void printlnStars(int num) {



    }
    public static void main(String[] args) {



    }
}

Question 0-2

Consider the following method to compute the greatest common denominator of two numbers.

public static int gcd(int m, int n) {
    int r;
    while(n != 0) {
        r = m % n;
        m = n;
        n = r;
    }
    return m;
}

Say we call gcd(32,20). Show how the values of r, m, and n change as the computer continues through the method.

r
m 32
n 20

Question 0-3

The following program uses the Account class we defined in class.

import csbsju.cs160.*;

public class PrintHello {
    public static void main(String[] args) {
        Account a = new Account();
        Account b = new Account();
        a.deposit(81.0);
        b.withdraw(3.0);
        a = b;
        a.deposit(9.0);
        b = new Account();
        b.withdraw(1.0);
        IO.println(a.getBalance());
    }
}

What does this program print?

Question 0-4

Consider the following class method.

public static void mystery(int[] arr) {
    for(int i = arr.length - 1; i > 0; i--) {
        arr[i] = 10 + arr[i - 1];
    }
    for(int i = 0; i < arr.length; i++) {
        IO.print(arr[i]);
    }
}

Suppose we were to pass the array { 1, 4, 5 } into this method. What would the method print?

Question 0-5

Define a new class Rect that can be used to create an object representing a rectangle. The constructor method for Rect should take two parameters, both doubles: the rectangle's width and the rectangle's height. The class should support the following object methods.

`double getPerimeter()`	Returns the length of the rectangle's perimeter.
`double getArea()`	Returns the area of the rectangle.
`boolean canContain(Rect other)`	Returns `true` if `other` can fit within the rectangle. (in its current configuration or rotated 90 degrees).

public class Rect {
    // your answer here...


}

Solutions

Solution 0-1

import csbsju.cs160.*;

public class PrintTriangle {
    public static void printlnStars(int num) {
        for(int i = 0; i < num; i++) IO.print("*");
        IO.println();
    }
    public static void main(String[] args) {
        IO.print("Width? ");
        int n = IO.readInt();
        for(int i = n; i > 0; i--) printlnStars(i);
    }
}

Solution 0-2

r 12 8 4 0
m 32 20 12 8 4
n 20 12 8 4 0

Solution 0-3

6.0

Solution 0-4

11114

Solution 0-5

public class Rect {
    private double width;
    private double height;

    public Rect(double w, double h) {
        width = w;
        height = h;
    }

    public double getPerimeter() {
        return 2 * width + 2 * height;
    }

    public double getArea() {
        return width * height;
    }

    public boolean canContain(Rect other) {
        return (width >= other.width && height >= other.height)
            || (width >= other.height && height >= other.width);
    }
}