#!/usr/bin/env python
# coding: utf-8

# # Conditionals - flow-control structures
# 
# - conditional statements control the flow of execution of codes
#     - makes some block of code to skip or execute based on some conditions
#     - loosely speaking, it helps computer think and make decision
# - boolean values - True or False
# - boolean expressions - comparison operators are used to compare values that result in True or False value.

# ## Comparison operators
# - allow us to compare data resulting in True or False outcome
# - ==, !=, >, >=, <, <=

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# Examples of various comparison operators
# x == y => True if x is equal to y
# x != y => True if x is not equal to y
# x > y => True if x is greater than y
# x < y => True if x is less than y
# x >= y => True if x is greater than or equal to y
# x <= y => True if x is less than or equal to y
x = 5
y = 10
print(x==y)
print(x!=y)
print(x>y)
print(x<y)
print(x<=y)
print(x>=y)


# ## Conditional execution
# - Three types of conditional selectors
# - One-way, Two-way and Multi-way selectors

# ## One-way selector
# - just one if statement by itself
# - syntax:
# ```python
# if <boolean expression> == True:
#     # execute this block of code
# ```

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if True:
    print('hello')


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if 'a' == 'a':
    print('a equals to a')


# ## Two-way selector
# - if statement followed by else statement
# - syntax:
# 
# ```python
# if <boolean expression> == True:
#     # execute this block of code
# else:
#     # do this
#     
# ```

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if 10 >= 20:
    print ('print 10 is greater than or equal to 20')
else:
    print ('print 10 is NO greater than or equal to 20')


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if 100.5 >= 100.5:
    print('True')
else:
    print('False')


# ## Multi-way selector
# - similar to multiple-choice questions with only one valid answer
# - start from first if statement and as soon as a if expression is evaluated True all the rest elif, else are ignored
# 
# ```python
# if <condition1>: 
#     # block1
#     # execute this...
# elif <condition2>:
#     # block2 
#     # execute this
# ... 
# ... 
# else: 
#     # else block
#     # execute code in this block
#     
# ```

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# Guess the number entered by user
ans = int(input('Enter a number between 1-5:'))
if ans == 1:
    print('You entered 1')
elif ans == 2:
    print('You entered 2')
elif ans == 3:
    print('You entered 3')
elif ans == 4:
    print('You entered 4')
elif ans == 5:
    print('You entered 5')
elif ans > 5:
    print('You entered a number larger than 5')
else:
    print('I do not know what you entered! Hmm....')


# ### Visualize using pythontutor.com: https://goo.gl/ZSm9KS

# ## Logical Operators
# **and**, **or**, and **not** -- allow to build more complex boolean expressions <br >
# 
# **Truth table for and**
# 
# | a | b  | a **and** b |
# | --- | --- | --- |
# | T | T |  T |
# |T | F |  F |
# |F | T |  F |
# |F | F |  F |
# 
# 
# **Truth table for or**
# 
# | a | b  | a **or** b |
# | --- | --- | --- |
# | T | T |  T |
# |T | F |  T |
# |F | T |  T |
# |F | F |  F |
# 
# **Truth table for not**
# 
# |a  |  not a |
# |---|---|
# |T  |   F |
# |F  |   T |
# 
# ### Order of Evaluations: Highest to Lowest: <br>
# http://www.informit.com/articles/article.aspx?p=459269&seqNum=11

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num = 10
if (num %2 ==0 and num > 0):
    print(num, "is positive and even")
    


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num = -14
if (num %2 ==0 and num < 0):
    print(num, "is negative and even")


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if not False:
    print('True')


# ## Exercises
# Exercise 1: Write a program to test whether a given whole number is even, odd or zero

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x = input('Enter a whole number:' )
x = int(x)
if x == 0:
    print(x, 'is zero')
elif x%2 == 0:
    print(x, 'is even')
else:
    print(x, 'is odd')


# Exercise 2. Improve the above program to tell whether the given whole number is positive or negative.

# Exercise 3. Write a program that helps someone decide where to go eat lunch depending on amount of money one has in their pocket.

# Exercise 4. Given a day of week as integer (say 1 for Sunday) write a program that tells whether that day is weekend, or weekday and the actual name of the day.

# ## Nested conditionals
# ```python
# if condition:
#     if condition1:
#         # do something
#     else:
#         # do something else
#         if condition2:
#             # do something...
# else:
#     # do this...
# 
# ```

# Exercise 5: Write a program that determines whether someone is eligible to vote in the US federal election.

# Exercise 6:
# <pre>
# Write a function day_name that converts an integer number 0 to 6 into the name of a day. Assume day 0 is “Sunday”. Once again, return None if the arguments to the function are not valid. Here are some tests that should pass:
# 
# 
# assert day_name(3) == "Wednesday"
# assert day_name(6) == "Saturday"
# assert day_name(42) == None
# </pre>

# Exercise 7:
# <pre>
# Write a function that helps answer questions like ‘“Today is Wednesday. I leave on holiday in 19 days time. What day will that be?”’ So the function must take a day name and a delta argument — the number of days to add — and should return the resulting day name.
# 
# Here are some tests that should pass:
# assert day_add("Monday", 4) ==  "Friday"
# assert day_add("Tuesday", 0) == "Tuesday"
# assert day_add("Tuesday", 14) == "Tuesday"
# assert day_add("Sunday", 100) == "Tuesday"
# assert day_add("Sunday", -1) == "Saturday"
# assert day_add("Sunday", -7) == "Sunday"
# assert day_add("Tuesday", -100) == "Sunday"
# </pre>

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