CPSC120B - Day 15 Notes

Computer Science Thing of the Day

M-blocks

Reading Questions

Quiz

quiz 15

Logical Operators

Numerical operators have numeric values for operands
Logical operators (or Booean operators) have boolean values for operands
```
print(True and False)
print(False or True)
print(not False)
```
These are useful in conditional statements when you have complex conditions

For example, if you want to check if a number is in a range

x = int(input('enter an integer: '))
if x >= 0:
    if x <= 9:
        print('you entered a single digit number')
    else:
        print('you did not enter a single digit number')
else:
    print('you did not enter a single digit number')

This can be simplified with a logical operator

x = int(input('enter an integer: '))
if x >= 0 and x <= 9:
    print('you entered a single digit number')
else:
    print('you did not enter a single digit number')

Note, the operands must be Booleans!

The following will not work

print(x == 1 or 2 or 3)
print(x > 0 and < 10)

Also note, and, or and not, do not have the same precedence
```
x = 2
print(not x == 1 or x == 2)
```
Is not equivalent to
```
x = 2
print(not (x == 1 or x == 2))
```

Boolean Functions

Can have variables equal to boolean values

x = int(input('enter an integer: '))
if x >= 0 and x <= 9:
    x_is_digit = True
else:
    x_is_digit = False
if x_is_digit == True:
    print('you entered a single digit number)
else:
    print('you did not enter a single digit number')

Setting a variable to a Boolean value can usually be simplified by using an expression

x = int(input('enter an integer: '))
x_is_digit = x >= 0 and x <= 9
if x_is_digit == True:
    print('you entered a single digit number)
else:
    print('you did not enter a single digit number')

This can make the code more readable
Note that if x_is_digit == True: is a little redundant

It can be simplified to if x_is_digit: which also reads a little better

x = int(input('enter an integer: '))
x_is_digit = x >= 0 and x <= 9
if x_is_digit:
    print('you entered a single digit number)
else:
    print('you did not enter a single digit number')

Can also do this with a function that returns a Boolean value

def is_digit(x):
    return x >= 0 and x <= 9
x = int(input('enter an integer: '))
if is_digit(x)
    print('you entered a single digit number)
else:
    print('you did not enter a single digit number')

Example - Point in Circles

import graphics

POINT_WIDTH = 10

# PRE:  point_x, point_y, circle_x, circle_y, and circle_radius are
#       positive numbers
# POST: returns whether the specified point is inside the specified
#       circle
def is_point_in_circle(point_x, point_y, circle_x, circle_y, circle_radius):
    delta_x = circle_x - point_x
    delta_y = circle_y - point_y
    distance = (delta_x * delta_x + delta_y * delta_y) ** (1 / 2)
    return distance <= circle_radius

circle_offset = 50
circle_1_x = graphics.window_width() / 2 - circle_offset
circle_1_y = graphics.window_height() / 2 
circle_1_radius = 100
circle_1_width = circle_1_radius * 2
circle_1_height = circle_1_width
circle_2_x = graphics.window_width() / 2 + circle_offset
circle_2_y = graphics.window_height() / 2 
circle_2_radius = 100
circle_2_width = circle_2_radius * 2
circle_2_height = circle_2_width

graphics.clear()
graphics.draw_oval(circle_1_x, circle_1_y, circle_1_width, circle_1_height)
graphics.draw_oval(circle_2_x, circle_2_y, circle_2_width, circle_2_height)
while graphics.window_open():
    if graphics.button_down(1):
        point_x = graphics.mouse_x()
        point_y = graphics.mouse_y()
        in_circle_1 = is_point_in_circle(point_x, point_y,
                                         circle_1_x, circle_1_y,
                                         circle_1_radius)
        in_circle_2 = is_point_in_circle(point_x, point_y,
                                         circle_2_x, circle_2_y,
                                         circle_2_radius)
        if in_circle_1 or in_circle_2:
            graphics.draw_oval(point_x, point_y, POINT_WIDTH, POINT_WIDTH,
                               fill="green")
        else:
            graphics.draw_oval(point_x, point_y, POINT_WIDTH, POINT_WIDTH,
                               fill="red")
    graphics.wait()

Lab

lab15