CSC111 Exercise Boolean Variables

--D. Thiebaut (talk) 09:02, 14 February 2014 (EST)

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Boolean Variables

Rewrite the following Python statements taking the boolean expressions in the if-statement and replacing them with boolean variables.

Example:

   x = int( input( "> " ) )
   if  x != 0:
       print( "statement 1 " )

would become

   x = int( input( "> " ) )
   isNot0 =  x != 0
   if  isNot0:
       print( "statement 1 " )

Exercise 1

   x = int( input( "> " ) )

   if x % 2 == 0 and x % 5 == 0:
        print( "statement 1" )

Exercise 2

   x = int( input( "> " ) )

   if x % 2 == 0 and ( x < -10 or x > +10 ):
        print( "statement 2" )

Exercise 3

   x = int( input( "> " ) )

   if x % 2 == 0 and ( x >= -10 and x <= +10 ):
        print( "statement 3" )

Exercise 4

Solve Exercise 3 by taking the solution for Exercise 2 and making the smallest of editing

Exercise 5

Assume that we are dealing with graphics, and a rectangle is on the screen with a top-left corner having coordinates (x1, y1) and a bottom right corner having coordinates (x2, y2). We assume these variables are defined outside the code section shown below.

   # get the location of the mouse in the window
   x = mouseX()
   y = mouseY() 

   if ( x < x1 ) or ( x > x2 ) or ( y < y1 ) or ( y > y2 ):
        print( "statement 5" )

Exercise 6

Same setup as Exercise 5: this time we want to write an if-statement that will print "statement 6" only if the mouse is inside the rectangle.

Mini Challenge

Don't try this with your computer. Just think about it and try to figure it out yourself:

Is the code below valid? If it is, what does it print?

if True:
   print( "Happy Valentine's Day!" )
else:
   print( "Happy Spring Break!" )

Evaluating boolean expressions

Assume exp1, exp2, exp3, exp4, and exp5 are boolean expressions that receive the values True or False. Which statement gets printed for:

• exp1, exp2, exp3, exp4, exp5 = True, False, False, True, True
• exp1, exp2, exp3, exp4, exp5 = False, False, True, True, True

exp1 =  ...    # an expression that evaluates to True or False
exp2 =  ...    # an expression that evaluates to True or False
exp3 =  ...    # an expression that evaluates to True or False
exp4 =  ...    # an expression that evaluates to True or False
exp5 =  ...    # an expression that evaluates to True or False

if   exp1 and ( ( exp2 or not exp3 )  or not ( exp4 and exp5 ) ):

    print( "statement 1" )

else:

    print( "statement 2" )

The test above is a good example of lazy evaluation!