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

# # Data Values & Types, Variables, Std I/O, Computations
# - A value is one of the fundamental things -- like a letter or number -- that a program manipulates. 
# - These values are classified into data types.
# 
# - In Python, there're mainly two data types: numbers and strings - numbers can be integer or float
# - Boolean (True/False) is also supported type!
# 

# ## first program - hello world!

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# First program
# This is a comment line...
# By Programmer info...
print('Hello world!')
# In python 2: print is a statement not a function
# print 'Hello World!' 


# ## comments
# - Programming languages provide a way to write comment along with the codes
# - Python uses # symbol to write a single line comment
# - comments are for humans/programmers to convey/explain what the code is doing or supposed to do
# - Python interpreter ignores the comments

# ## data types
# - built-in type() function can be used to know type of data
# - functions will be covered in Chapter 04

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type(100)


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type(1000.99)


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type('Hello World!')


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type('A')


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print hello


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type("17")


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type("""Triple double quoted data""")


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type('''Type of Triple single quote data is''')


# ## type conversion/casting
# - changing data from one type into another when possible
# - use built-in function such as str(), int(), float(), etc. to convert data to that particular type
# 

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data = 'hello' # can't conver it to int or float types


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data = '100'
type(data)


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num = int(data)
type(num)


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price = float('500.99')
type(price)


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num = 99.99
strNum = str(num)
type(strNum)


# ## standard output
# - printing or writing output to common/standard output such as monitor
# - way to display the results and interact with the users of your program

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print('''"Oh no", she exclaimed, "Ben's bike is broken!"''')


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print("What\'s up\n Shaq O\'Neal?")


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type(True)


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print(x)


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help(str)


# ## escape sequences
# - some letters or sequence of letters have special meaning to Python
# - single, double and tripple single or double quotes represent string data
# - use backslash \ to represent these escape sequences, e.g.,
#     - \n - new line
#     - \\ - back quote
#     - \t - tab
#     - \r - carriage return
#     - \' - single quote
#     - \" - double quote

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print('hello \there...\n how are you?')


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print('how many back slahses will be printeted? \\\\')


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print(r'how many back slahses will be printeted? \\\\')


# ## variables
# - Variables are identifiers that are used to store values which can be then easily manipulated
# - variables give names to data so the data can be easily referenced by their names over and again
# - Rules and best practices for creating identifiers and variable names:
#     - can't be a keyword -- what are the built-in keywords?
#     - can start with only alphabets or underscore ( _ )
#     - can't have symbols such as $, %, &, white space, etc.
#     - can't start with a digit but digits can be used anywhere else in the name
#     - use camelCase names or use _ for_multi_word_names
#     - use concise yet meaningul and unambigous names for less typing and avoid typos

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help('keywords')


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help('True')


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# Define some variables to show the values stored in variables can be changed from one type to another
# Python is loosely typed


# ## computation - operators and operands
# - **operators** are special tokens/symbols that represent computations like addition, multiplication and division 
# - the values an operator uses are called **operands**
# - some binary operators that take two operands
#     - addition: 10 + 20
#     - subtraction: 20 - 10 
#     - true division: 10 / 3 
#     - integer division: 10 // 3 
#     - remainder: 10 % 2
#     - power: 2 ** 3

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# play with some examples of various operators supported by Python


# ## order of operations
# <strong> depends on the rules of precedence: PEMDAS from high to low order </strong><br />
# 1. Parenthesis
# 2. Exponentiation
# 3. Multiplication and Division (left to right)
# 4. Addition and Subtraction (left to right)
# 

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# some examples
print(2 * 3 ** 2)


# ## operations on string
# - Chapter 08 covers more on string data type

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help(str)


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# some examples
name = "John"
print(name, 'islower', name.islower())
print(name, 'isalpha', name.isalpha())
print(name, 'upper', name.upper())
print(name.zfill(10))
print(name.swapcase())
print(name.startswith('j'))
print(' hello world'.split())
print('hello$world'.split('$'))


# ## standard input
# - read data from standard or common input such as keyboards
# - allows your program to receive data during program execution facilitating user interactions

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name = input('What is your name? ')


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num = input('Enter a number =>')
print('You entered: ', num)


# ## composition
# - break a problem into many smallers sub-problems or steps using high-level algorithms
# - incrementally build the solution using the sub-problems or steps

# ### exercise
# 
# write a program that finds area and perimeter of rectangle

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# Demonstrate composition step by step
# Algorithm steps


# ### excercise
# write a program that finds perimeter and area of a circle.</p>
# <img src="http://openbookproject.net/thinkcs/python/english3e/_images/circle_area.png" />

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# Demonstrate composition step by step
# Algorithm steps