CS midterm 2

Question 1

variable

Answer 1

• Symbolic name used to refer to a value
• The value may change, but the symbolic name doesn’t
• Variables make code easier to change and easier to read
• Eg. MouseX is a variable
• We’re storing values “in them” and then using them like numbers

Question 2

using variables

Answer 2

• We don’t always know the value (or even care what the exact value is), we just refer to it with a name

Question 3

types of variables

Answer 3

•	Built-in Variables 
o	Eg. Width, mouseX
•	Constants
o	Eg. TWO_PI, BEVEL
•	User-defined Variables
o	Eg. donutSize, bgShade

Question 4

math expressions

Answer 4

• • add
• • subtract… negative numbers
• • multiply
• () order of operations
• / divide… divide by zero error… truncation behaviour
• % modulo (remainder after division)

Question 5

demos

Answer 5

• int x = 10
• x = x * 20 (10 x 20 = 200)
• printIn(x);
• x is the variable

Question 6

creating user-defined variables

Answer 6

• int donutSize = 80; = variable declaration statement
• int = variable data type
• donutSize = variable name
• = 80; = value assignment

Question 7

variable data types

Answer 7

• int – “integer”, whole numbers like -5, 0, 12
• float – “floating point”, decimal numbers like 0.123, -10.1, 32.0, 0.0
• Boolean – true or false
• String – any literal text, eg. “hello”, “123”, “yoko ono”, etc.
• Char – one character, eg. ‘a’, ‘4’
• Color – a processing colour
• …many more types

Question 8

declaring and assigning variables

Answer 8

•	Declaring: 
o	int donutSize;
•	Assigning:
o	donutSize = 80;
•	Declaring and Assigning (aka “Initializing”):
o	int donutSize = 80;

Question 9

why user defined variables

Answer 9

• To reuse the same value in your program
o Eg. Draw many squares of same size
• To make it easy to change a value later
o Eg. Make squares larger
• To make your code easier to understand
o Eg. Easier to read code since “squareSize” means more than “10”
• Keep tracking of something that changes
o Eg. Click number, animation

Question 10

(key/mouse)PressNumber

Answer 10

• Keep track of mouse and key presses with user-defined variables
• Also…
• textAlign(horz, vert); (or CENTER, CENTER)
• text(s, x, y);

Question 11

functions that return a value

Answer 11

•	Some functions return a value, like random()
•	You can assign the “result” of these functions to a variable
o	float x = random(100);
•	You can also use them as an argument for another function
o	point(random(width), random(height));

Question 12

int and float conversion

Answer 12

• You can assign an int to a float:
o float f = 1;
• You cannot assign a float to an int
o int y = 0.5; // error! 0.5 is a float
o int r = radians(45); // error! Radians returns a float
o int hue = random(360); // error! Random returns a float
• You can convert a float to int using the int() function
o int y = int(0.5);
o int r = int(radians(45));
o int hue = int(random(360));

Question 13

custom variables

Answer 13

•	Tend to declare variables at the beginning before we do anything else
•	Example:
o	int donutSize = 80;
o	int bgShade = 200; // light gray
•	After declaring variables, they can be used anywhere throughout the program
o	void setup() {
o	size(100, 100);
o	background(bgShade);
o	}

Question 14

boolean expressions

Answer 14

an expression that evaluates to true or false

!= number is not equal to 99

<= number is less than or equal to

> = number is greater than or equal to

== number is equal to

< number is greater than

> number is less than

Question 15

conditional statement

Answer 15

if a boolean expression is true, than execute a block of code

Question 16

rest stop analogy

Answer 16

• A single if statement is like deciding to stop at a rest stop on a highway

Question 17

detour analogy

Answer 17

• if else is like having to take a detour (the if) or taking the original road (the else)

Question 18

two common logic errors with if statements

Answer 18

• Adding semicolon after the Boolean expression means no code block. A code block with no “if” means always execute.
• Missing “else” makes two if statements.

Question 19

equality vs. assignment operators

Answer 19

• Equality Operator ==
o Is the left value equal to the right value?
o Eg. State == 1 means “is state equal to 1?”
o Left and right can be anything that reduces to a single value (a variable, a function that returns a value, a number, an expression)
• Assignment Operator =
o Assign the right value to the left variable
o Eg. State = 1 means “assign 1 to state”
o Left must be a variable, right can be anything that reduces to a single value (a variable, a function that returns a value, a number, an expression)

Question 20

Numerical Representation: Integers

Answer 20

•	Binary Numbers: 1 and 0
•	Bits and Bytes
•	Integer Representation: 
o	Fixed size
o	How to handle negative numbers?
•	Use println statements to find errors

Question 21

Numerical Representation: Float

Answer 21

• 0.0001 meters is a huge difference for a microchip designer, though all measurements will be less than about 0.1 meters

Question 22

numerical precision

Answer 22

• How many numbers are there between 0 and 1?
• How many decimal points in one-third(1/3)?
• Computers can not always do exact math
• This has implications for equality testing…

Question 23

logical operators

Answer 23

• && means “and”
• || means “or”
• ! means “not”

Question 24

mousePressed

Answer 24

• An event function
o Called once when the mouse button is pressed
• mousePressed is a built-in Boolean variable
o true when the mouse button is pressed, false otherwise
• Same for keyPressed and keyPressed()