Quiz 1 Review

Problem Q1r.1.

Suppose the computer executes the below program fragment, with the user typing 50 when prompted. Sketch what path will be left in the window when the program reaches its end.

double x;
x = this.readDouble();
Turtle t;
t = new Turtle(10, 100);
t.forward(x);
t.left(90);
t.forward(20);
t.right(90);
t.forward(x);
t.hide();

Problem Q1r.2.

Suppose we have an int variable named k with a value of 31. What is the value of each of the following expressions?

Problem Q1r.3.

Suppose we have two variables — an int variable named k with the value of 18, and a double variable named x with the value of 3.5. What is the value of each of the following Java expressions?

Problem Q1r.4.

List the values of a, b, and c following the execution of the below fragment.

int a = 10;
int b = 20;
int c = 40;

a = b;
a = c;

Problem Q1r.5.

List the values of a, b, and c following the execution of the below fragment.

int a = 10;
int b = 20;
int c = 40;

a = b;
b = c;
c = a;

Problem Q1r.6.

Give two examples seen in class of each of the following.

a. primitive types
b. classes

Problem Q1r.7.

Name one way in which programs work differently with primitive types (such as int, double, and boolean) than with classes (basically all other types). Give an example of one type in each category.

Problem Q1r.8.

In the below program fragment, draw a circle around each variable initialization, and draw a rectangle around each variable declaration.

int a;
int b;
a = 95;
b = 40;
while(b != 0) {
    int r;
    r = a % b;
    a = b;
    b = r;
}

Problem Q1r.9.

List the values taken on by the variables a and b as the computer executes the below program fragment.

int a;
int b;
a = 95;
b = 40;
while(b != 0) {
    int r;
    r = a % b;
    a = b;
    b = r;
}

Problem Q1r.10.

Sketch the final appearance of the window when the computer completes the program below.

Turtle t;
t = new Turtle(20, 75);
int drawn;
drawn = 0;
while(drawn < 5) {
    t.forward(65);
    drawn = drawn + 1;
    t.left(72);
    t.forward(65);
    t.right(144);
}
t.hide();

Problem Q1r.11.

Suppose we wish to repeat the below while loop until the square of x is between 99 and 101. What condition belongs in the parentheses?

while(                                ) {
    x = (x + 1.0 / x) / 2.0;
}

Problem Q1r.12.

The below program fragment creates a circle that moves right continually. Modify it so that the circle moves right for 100 frames and then stops.

GOval circle = new GOval(100, 100, 20, 20):
this.add(circle);



while(true) {
    this.pause(40);


    circle.move(1, 0);


}

    GOval circle = new GOval(100, 100, 20, 20):
    this.add(circle);

    int frames = 0;
    while(true frames < 100) {
        frames++;
        this.pause(40);
        circle.move(1, 0);
    }

Problem Q1r.13.

Using the GOval class, complete the program fragment below so that it draws n circles of diameter 10 stacked on top of each other. For example, if the user enters the number 8, the program would display the following.

(The circles' coordinates are not important, as long as the circles are stacked atop one another.)

int n;
n = this.readInt();

int drawn;
drawn = 0;
while(drawn != n) {
    GOval circle;
    circle = new GOval(50, 10 + 10 * drawn, 10, 10);
    this.add(circle);
    drawn = drawn + 1;
}

Problem Q1r.14.

Below is a program that draws a circle which slowly falls down the window. Indicate the program so that the circle accelerates as it falls. That is, it should fall by 1 pixel for the first frame, 2 pixels for the second, 3 pixels for the third, and so on. (Don't worry about what happens when it reaches the window's bottom: It should keep falling forever.)

public class DropBall extends GraphicsProgram {
    public void run() {
        GOval ball = new GOval(250, 0, 50, 50);
        this.add(ball);



        while(true) {
            this.pause(20);



            ball.move(0, 1);

        }
    }
}

public class DropBall extends GraphicsProgram {
    public void run() {
        GOval ball = new GOval(250, 0, 50, 50);
        this.add(ball);

        int dy = 1;
        while(true) {
            this.pause(20);
            ball.move(0, 1 dy);
            dy++;
        }
    }
}