CS 10: Introduction to Computer Programming

In-Class Examination 1

Closed-Book, 75 minutes, Winter 1998

General Instructions

Before you answer any questions, write your name and perm number.
Read each question carefully. Make sure that you clearly understand each question before answering it.
Put your answer to each question on its own page.
Use a pen to write your answer. You may wish to work out an answer on scratch paper before writing it on your answer page; answers that are difficult to read may lose points for that reason.

Question	Value
1	20
2	20
3	15
4	20
5	25
Total	100

1. What is the value of variables i, j, and k at point A) and B) below?

int i = -7, j = i*i, k = j%5;

// A) what is the value of i, j, and k at this point?

    i *= i + 1;
    j %= i-- + 5;
    k /= i = j + ++i;
    // B) what is the value of i, j, and k at this point?

Solution:

A) i = -7, j = 49, k = 4

B) i = 44, j = 2, k = 0

2. In the applet skeleton below, interpret the int variables x (horizontal coordinate) and y (vertical coordinate) to be the coordinates of a point. Complete the following skeletal applet so that it paints a filled square whose upper left corner is at coordinates (100, 100). The square should be 100 X 100, and colored:

black if the point (x, y) is somewhere in the square whose upper left corner has coordinates (100, 100) and whose lower right corner has coordinates (200, 200).
red otherwise.

Assume that variables x and y already have values.

import java.awt.*;

import java.applet.*;

public class test extends Applet {

public void paint(Graphics g) {

int x,y;

}

Solution:

// I did not expect you to use boolean operators.

import java.awt.*;

import java.applet.*;

public class test extends Applet {

public void paint(Graphics g) {

int x,y; // Assume that variables x and y already have values.

g.setColor(Color.red);

if (100 <= x)

if (x <= 200)

if (100 <= y)

if (y <= 200)

g.setColor(Color.black);

g.fillRect(100,100,100,100);

}

3. Convert the following sequence of Java statements to an equivalent sequence without for statements. You may use while statements. If this cannot be done, explain why.

for (int i = 1; i < 100; i *= -3)

for (int j = 1; j < 100; j *= -2) {

g.fillRect(X + j*5, Y + i*5, 5, 5);

}

Solution:

int i = 1, j;

while (i < 100) {

j = 1;

while (j < 100) {

g.fillRect(X + j*5, Y + i*5, 5, 5);

j *= -2;

}

i *= -3;

}

4. Complete the following skeletal applet so that it computes, into a variable called sum, the sum of all numbers between 10 and 60 that are not evenly divisible by 2, 3, 5, and 7. Output the value of sum somewhere on the applet using the drawString command.

import java.awt.*;

import java.applet.*;

public class test extends Applet {

public void paint(Graphics g) { ... }

}

Solution:

import java.awt.*;

import java.applet.*;

public class test extends Applet {

public void paint(Graphics g) {
int sum = 0;

        for (int i = 10; i <= 60; i++) {
            if (i % 2 != 0)
                if (i % 3 != 0)
                    if (i % 5 != 0)
                                            if (i % 7 != 0)
                        sum += i;
        }
    }
}

5. Complete the following skeletal applet so that it paints 2 triangular stacks of circles, as shown (on the monitor during the exam). Each circle is 10 pixels in diameter and is separated by 2 pixels from the circles around it. The triangles are identical except the left one starts at the left side of the applet; the right triangle starts at horizontal coordinate 200. Each triangle has 15 rows. The triangles are colored the same: Circles in the same column have the same amount of red. Each circle has no green and no blue. The amount of red in a column is 255/15 more than the column to its left. The leftmost column has no red.

import java.awt.*;

import java.applet.*;

public class test extends Applet {

public void paint(Graphics g) { ... }

}

Solution:

import java.awt.*;

import java.applet.*;

public class test extends Applet {

public void paint(Graphics g) {

        for (int X = 0; X <= 200; X +=200)
        for (int row = 0; row < 15; row++)
        for (int col = 0, red = 0; col < 15 - row; col++, red += 255/15) {
            g.setColor(new Color(red, 0, 0));
            g.fillOval(X + col*12, row*12, 10, 10);
        }
    }
}