Quiz 4: Study Guide

Quizzes are open book. 30 minutes at the start of class.

Topics:

This quiz includes the previous topics from Quiz 1, 2 and 3 plus

  • arrays

  • classes

    • defining and using classes

    • terms: methods, member variables, accessors (getters), mutators (setters)

    • scope of member variables

General quiz self-assessment:

  • Can you define terms?

  • Are you familiar with the Processing functions we use in class and labs?

  • Do you know the syntax for defining and using variables, if statements, loops, functions, and classes?

  • Can you read and understand code? Could you spot errors? Can you trace the execution and deduce the values for all variables?

  • Can you write code which solves a given problem? Can you solve it in different ways? For example, if a question asks you to use a function, can you solve the problem using a function?

Practice questions

1) Loop practice. Can you write loops in setup() which produce the following console output?

  • Write a loop that prints the following sequence to the console

The next number is:  -5
The next number is:  -4
The next number is:  -3
The next number is:  -2
The next number is:  -1
The next number is:  0
The next number is:  1
The next number is:  2
The next number is:  3
The next number is:  4
The next number is:  5

  • Write a loop that prints the following sequence to the console

X =  10.0
X =  20.0
X =  30.0
X =  40.0
X =  50.0
X =  60.0
X =  70.0
X =  80.0
X =  90.0

  • Write a program that outputs the following to the console

10
9
8
7
6
5
4
3
2
1
Blast off!

  • Write a program that outputs the following pattern to the console

*
**
***
****
*****

  • Write a program that outputs a 5x5 square of asterisk to the console

*****
*****
*****
*****
*****

2) Loop practice. Use loops to compute quantities over random numbers.

  • Using a loop, compute the sum of 5 random numbers between -10 and 10. Output the results to the console. Below is an example

9.732847
3.099474
-9.973539
2.9620247
-6.101103
Sum: -0.28029633

  • Using a loop, compute the maximum value of 5 random numbers between -10 and 10.

3) Function practice. Write functions corresponding to the following specifications. For each question, test your function from setup() using an array of random values as input. Your function should not hard-code the length of the array. You should also print the result to the console.

  • Write a function that converts miles to kilometers. There are 1.609 kilometers in a mile. Test your function with the following sequence of values using a loop: 1.0, 1.25, 1.5, 1.75, 2.0, …​, 3.0.

// Implement function: milesToKilometers
// Input: miles (float)
// output: kilometers (float)

  • Write a function that computes the tip.

// Implement function: computeTip
// Input: total cost (float)
// Input: tip percent (float)
// Output: float

  • Write a function that computes the average of an array of numbers

// Implement function: computeAverage
// Input: values (array of float)
// Output: float

  • Write a function that returns true if an array of float has a negative number on it.

// Implement function: containsNegative
// Input: values (array of float)
// Output: boolean

  • Write a function that reverses the contents of an array. (Hint: create and return a new array in the function)

// Implement function: reverseArray
// Input: values (array of float)
// Output: values (array of float)

4) Class practice.

  • Implement a Movie class. Movie should contain the following data and methods

// Data

// Title (string)
// Duration in minutes (float)
// Year (integer)
// actors (array of String)

// Methods

// Constructor
// Input: Title (string)
// Input: Duration in minutes (float)
// Input: Year (integer)
// Input: actors (array of String)

// Accessor for title
// Mutator for title

  • Test your Movie class. Create a Movie object for "The Shining" which was made in 1980, is 2 hours and 26 minutes long, and stars Jack Nicholson and Shelley Duval. Create your object in setup()

5) Write a program that produces the following image using loops.

Q4 loops 5x3

6) A programmer has a bug in her code. She expected compute to return 4.0 but it’s returning 3.0. What’s wrong?

float compute(float a, float b, float c) {
  float tmp = a + b;
  return tmp - c;
  tmp += 1.0;
}

void setup() {
  float result = compute(1.0, 4.0, 2.0);
  println(result);
}

7) Consider the following program

int mystery(int[] values) {
  int total = 0;
  for (int i = 0; i < values.length; i++) {
    int value = values[i];
    if (values[i] < 0) {
      value = -value;
    }
    total += value;
    println("mystery: ", value, total);
  }
  return total;
}

void setup() {
  int[] values = {-1, 0, 1, 2, 3};
  println("Checkpoint 1:", values[2]);

  int result = mystery(values);
  println("Checkpoint 2: ", result);
}

  • What is the output of this program?

  • What local variables are in scope in setup()?

  • What local variables are in scope in mystery()?

  • What is the return type of mystery()?

8) Consider the following program

String snaf(int a) {
  if (a < 5) {
    return "pop";
  }
  else {
    return "crackle";
  }
}

int fee(int q) {
  return -q;
}

int bar(int u, int v) {
  return -10*u + fee(v);
}

int foo(int x, int y) {
  return x*10 - fee(y);
}

void setup() {
  int a = -5;
  int b = 5;
  int c = 10;
  int d = foo(a, b);
  int e = bar(b, a);
  String result = snaf(d+e);
  println(result, d, e, d+e);
}

  • What console output is produced by this program?

10) Consider the following program

void setup() {

  Mystery m1 = new Mystery(4,1);
  Mystery m2 = new Mystery(1,1);

  int result1 = 0;
  int result2 = 0;
  result1 = m1.compute(2);
  result2 = m2.compute(2);
  println("BEFORE compute1: ", result1);
  println("BEFORE compute2: ", result2);

  m1.setA(3);
  m2.setB(3);

  result1 = m1.compute(2);
  result2 = m2.compute(2);
  println("AFTER compute1: ", result1);
  println("AFTER compute2: ", result2);
}

where Mystery is defined as

class Mystery {

  int a = 0;
  int b = 0;

  Mystery(int x, int y) {
    a = x;
    b = y;
  }

  void setA(int x) {
    a = x;
  }

  void setB(int y) {
    b = y;
  }

  int compute(int factor) {
    return a + factor*b;
  }
}

  • What is the console output of this program?

  • What constructors are defined in this program?

  • What member variables are defined in this program?

  • What variables are in scope in Mystery’s compute method?

  • What methods are defined in Mystery?

  • Implement an accessor method for the attribute (e.g. member variable) a in Mystery.

Answers

1)

for (int i = -5; i <= 5; i++) {
   println("The next number is:", i);
}
for (float i = 10; i < 100; i+=10) {
   println("X =", i);
}
for (int i = 10; i > 0; i--) {
   println(i);
}
println("Blast off!")
// Using an accumulator
String s = "*";
for (int i = 0; i < 5; i++) {
   s += "*";
   println(s);
}
// Using print statements, rather than an accumulator
for (int i = 0; i < 5; i++) {
   for (int j = 0; j < 5; j++) {
      print("*");
   }
   println();
}

2)

float total = 0.0;
for (int i = 0; i < 5; i++) {
  float value = random(-10,10);
  total += value;
  println(value);
}
println("Sum: ", total);
float total = 0.0;
for (int i = 0; i < 5; i++) {
  float value = random(-10,10);
  total += value;
  println(value);
}
println("Sum: ", total);
float maxValue = -11.0;
for (int i = 0; i < 5; i++) {
  float value = random(-10,10);
  if (value > maxValue) {
    maxValue = value;
  }
  println(value);
}
println("Max: ", maxValue);

3)

// Implement function: milesToKilometers
// Input: miles (float)
// output: kilometers (float)
float milesToKilometers(float m) {
  float km = m * 1.609;
  return km;
}

void setup() {
  for (float m = 1.0; m <= 3.0; m += 0.25) {
    float result = milesToKilometers(m);
  }
}
// Implement function: computeTip
// Input: total cost (float)
// Input: tip percent (float)
// Output: float
float computeTip(float totalCost, float percent) {
  float tip = totalCost * percent;
  return tip;
}
// Implement function: computeAverage
// Input: values (array of float)
// Output: float
float computeAverage(float[] values) {
  float total = 0.0;
  for (int i = 0; i < values.length; i++) {
    float value = values[i];
    total += value;
  }
  return total / values.length;
}
// Implement function: containsNegative
// Input: values (array of float)
// Output: boolean
boolean containsNegative(float[] values) {
  for (int i = 0; i < values.length; i++) {
    if (values[i] < 0) {
      return true;
    }
  }
  return false;
}
// Implement function: reverseArray
// Input: values (array of float)
// Output: values (array of float)
float[] reverseArray(float[] input) {
  float[] result = new float[input.length];
  for (int i = 0; i < input.length; i++) {
    int reverseIdx = input.length - i - 1;
    result[reverseIdx] = input[i];
  }
  return reverseIdx;
}

4)

class Movie {
  String mTitle;
  float mDuration;
  int mYear;
  String[] mActors;

  // Constructor
  Movie(String title, float duration, int year, String[] actors) {
    mTitle = title;
    mDuration = duration;
    mYear = year;
    mActors = actors;
  }

  // Accessor for title
  String getTitle() {
    return mTitle;
  }

  // Mutator for title
  void setTitle(String title) {
    mTitle = title;
  }
}

And below is code to test the class

void setup() {
  float minutes = 2*60 + 26;
  String[] actors = {"Jack Nicholson", "Shelley Duval"};

  // Be careful to list parameters in the correct order!
  // They must match the inputs to the constructor
  Movie theShining = new Movie("The Shining", duration, 1980, actors);
}

5)

void setup() {
  size(600, 600);

  int numRows = 3;
  int numCols = 5;
  int size = 100; // size of each circle
  for (float y = size/2; y < numRows*size; y += size) {
    for (float x = size/2; x < numCols*size; x += size) {
      ellipse(x, y, size, size);
    }
  }
}

6) No code is executed after a function returns. Therefore, the line tmp += 1.0 is not executed in the function compute.

7)

  • Run the program to test the output

  • values, result

  • values, total, i, value

  • integer

8) Run the program to check your answer

9)

  • Run the program to test the output

  • Mystery contains one constructor which takes x and y as input

  • a, b

  • a, b, factor

  • setA, setB, compute, Mystery (the constructor) *

class Mystery {

  int a = 0;
  int b = 0;

  Mystery(int x, int y) {
    a = x;
    b = y;
  }

  // The accessor for a
  int getA() {
    return a;
  }
  // End added code

  void setA(int x) {
    a = x;
  }

  void setB(int y) {
    b = y;
  }

  int compute(int factor) {
    return a + factor*b;
  }
}