CPSC120B
Fundamentals of Computer Science I

Day 14 Notes

Conditionals

No Cool Computer Science Thing of the Day

Reading Questions

Quiz

quiz 14

Booleans

The Boolean type has only 2 values, True and False

Boolean expressions evaluate to Boolean values

print(1 == 2)
print(1 != 2)
print(1 < 2)
print(1 > 2)
print(1 <= 2)
print(1 >= 2)

Conditionals

Write code that executes only if a condition is met

Boolean values are useful for specifying the conditions

integer = int(input('enter an integer: '))
if integer == 0:
    print('You entered Zero')
else:
    print('You did not enter Zero')

Can also leave off the else
This can be toublesome if a variable is created in the if block
```
x = 0
if x != 0:
    y = x
print(y)
```

Graphics User Input

Graphics module has functions for getting mouse and keyboard input
The ‘wait’ function are blocking functions, the program stops running until user input
```
gaphics.wait_for_button_press()
graphics.draw_oval(0, 0, 100, 100, fill="black")
```
Can also get the current mouse state
```
graphics.mouse_x()
graphics.mouse_y()
```

But this isn’t useful unless repeatedly checking the value inside of a loop

for i in range(100):
    x = graphics.mouse_x()
    y = graphics.mouse_y()
    graphics.clear()
    graphics.draw_oval(x, y, 100, 100, fill="black")
    graphics.wait()

This runs a fixed number of frames, it would be better to run as long as the user wants

while graphics.window_open():
    x = graphics.mouse_x()
    y = graphics.mouse_y()
    graphics.clear()
    graphics.draw_oval(x, y, 100, 100, fill="black")
    graphics.wait()

Can also get the button state

x = 0
y = 0
while graphics.window_open():
    if graphics.button_down(1):
        x = graphics.mouse_x()
        y = graphics.mouse_y()
    graphics.clear()
    graphics.draw_oval(x, y, 100, 100, fill="black")
    graphics.wait()

The 1 argument to the button_down function tests if the left mouse button is down

Lab

lab14