# -*- coding: utf-8 -*-

# Rodrigo Muñoz

# 6.S189 Lecture 2

# Conditional Operators, Branching







# =====================

# Conditional Operators

# =====================

# So far we've learnt about +-*/ etc...

# These take in a number and return another number

# Remeber: Boolean types. True or False. (Note distinct lack of quotes. These are not strings!)

# New operators: >, >=, <, <=, ==, !=



# Examples, greater than, less than:

print "Conditional Operators:"

print "9 > 5:", 9 > 5

print "15 < 9:", 15 < 9



# == is a logical "equals"

# returns True if both items are equal, False otherwise

# VERY IMPORTANT: "=" is assignment operator. "==" is the comparison operator.



print "7 == 7:", 7 == 7

print "7.0 == 7:", 7.0 == 7

print '"apple" == "orange":', "apple" == "orange"

print "True == False:", True == False



# analogously, != is a logical "not equal to"

print "type(0.5) != type(True):", type(0.5) != type(True)



# As with other stuff, we can store results to variables

bool1 = 3 > 2

print "bool1 = 3 > 2"

print "bool1 =", bool1



# There are some other operators we can use for boolean logic

# These are "and", "or", and "not"

# a and b is true if a is true and b is true

# a or b is true if either a or b are true

# not a is true if a is false



print "True and True:", True and True

print "True and True and False:", True and True and False

print "True or False:", True or False

print "False or False or True:", False or False or True

print "not False:", not False







# =============================

# Branching (aka if statements)

# =============================



# Branching allow us to run certain instructions if a particular condition is met



if "apples" != "oranges":

    print "All systems in order!"



# Note: If can be all by itself, if the else clause would be "do nothing"



myGrade = "Failing"

if myGrade == "Passing":

    print "Yay!"

else:

    print "D'oh!"



yourGrade = raw_input("What's your grade? ")

if yourGrade == "P":

    print ":D"

elif yourGrade == "D":

    print ":|"

elif yourGrade == "F":

    print ":("

else:

    print "Wait, what?"



# Note that the order of evaluation matters!

# If at all possible, make it such that only one conditional can be true at once!

# In the example below, we'd want the code to output "It's freezing.", but since the

# conditionals are evaluated in order, we are actually outputting "It's not that bad."



temperature = 30

if temperature < 70:

    print "It's not that bad."

elif temperature < 50:

    print "Okay, it's a bit chilly."

elif temperature <= 32:

    print "It's freezing."



# Also note, it's perfectly fine for a conditional statement not to have an else statement.