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

# In[7]:


# Question -- if we run the following code and then
# try to run the code below ("print") before we give
# the response to the input box, then the code below
# doesn't run. How to fix it?
# Answer: use the "stop" button at the top to terminate
# the code looking for an input from the user
# worst case: save then "close and halt" from the File
# menu and try again
variable=input("question")


# In[10]:


print("program")


# In[21]:


# finish up Section 2.7
# How does mixing data types in python arithmetic work?
x=5
y=1.0
# 1. Operations involving only ints will return an int if possible.
# 2. Operations with only floats will return a float
# 3. Mixed operations default to returning a float
print("x+x=",x+x)
print("type(x+x)=",type(x+x))
print("x+y=",x+y)
print("type(x+y)=",type(x+y))
print("type(x)=",type(x))
print("type(float(x))=",type(float(x)))
print("type(x)=",type(x))
z=float(x)
print("type(z)=",type(z))


# In[36]:


# Section 2.8 -- more about data output
# We know already: the following code will print A, B, and C
# each on a new line.
print('A')
print('B')
print('C')
print('---------------')
# An option for the print function: end
print('A',end=".")
print('B',end=" ")
print('C',end="\n")
print('D',end="\n")
print('-----------')
x='a string of characters'
print('x=',x,"and also don't forget that x=",x)
print('x=',x,"and also don't forget that x=",x,sep='1234')


# In[37]:


# Section 2.9 -- named constants
# Imagine: you are hired by a bank to write code
# you open the code and see the following:
account=5.00
fee=account*0.069 # <-- this 0.069 number is mysterious -- no clear
                    # indication from the code of what its purpose is
                    # such mysterious numbers are called "magic numbers"
# better to use a "Named constant" which is just a variable that 
# describes its purpose, usually in all capitals to distinguish it to the eye
FEE_RATE=0.069
fee=account*FEE_RATE

print("11>>1=",11>>1)
# Great example of a magic number: source code of Quake III Arena
# Here is the procedure used by the programmers of this game to compute 1/sqrt(x):
# 1. get x
# 2. shift x right by 1 --- x>>1
# 3. subtract x>>1 from the magic number 0x5F3759DF
# 4. apply one step of Newton's method to increase precision
# read more: https://en.wikipedia.org/wiki/Fast_inverse_square_root