# This is code which would help you to start programming with python!

# Lines which start with # are COMMENTARY: everything typed after
# the first hash sign is ignored until the end of the line.

print("Hi!") # you can put your commentary after code too!

#-----------------------------------------------------------------------------
# We should start with a few important concepts:
# 1. VALUES: the simplest types of values are numbers and strings.
# Numbers can be integers or floating point numbers.
# The distinction is often very important so bear it in mind.

print("We are going to print some numbers now")
print(4) # an integer
print(5.01) # a floating point number

# You can use the usual mathematical operations with numbers:
# What type of number will be results of these operations?

print(4+10)
print(4-10)
print(4.-10)
print(4*10)
print(4.0*10)
print(4/10)
print(4.26*(-17.83))


# Strings are simply bits of text contained between quotation marks:
print("\nWe are going to print some strings now") # \n adds new line

print('Hello, world!')
print("Hello, world!")
# Take care to be consistent! You should open and close with
# the same quotation marks!

# You can concatenate strings using '+' sign:
print("alpha")
print("alpha"+"beta")
print("alpha"+" "+"beta")

# 2. EXPRESSIONS: a sequence of operations, functions and value which can be
# evaluated ("solved") to have a value of its own. All arithmetic examples from above
# are expressions. A single value can be thought of as an expression too!
# As you might have notice, print() only prints the value (i.e. solution) of
# your expression. Compare:

print("\nLet's look at some expressions and their values")
print("Expression: (12+18)*10")
print((12+18)*10)
print("Expression: 200+20*5")
print(200+20*5)

#---------------------------------------------------------------------

# 3. VARIABLES: a variable can be thought of as a box with a label
# (the name of the variable) into which you can put a  value.
# You assign the value to a variable using the '=' sign:
a = 3
# To the left of the equal sign is the name of the variable,
# to the right - the value it has from now on. 

# Whenever you use the variable's name,
# its value will be substituted, for example:
print("print variable a: ")
print(a)
b = 5
print("print the sum of variables a and b: ")
print(a+b)
print("print the mixed expression of variables and simple values: ")
print(13-a+b*4)

# The name of a variable should start with a letter or an underscore,
#and you can use letters, numbers and underscore. Upper and lower case matter!
my_variable = 3
My_variable = 5
MyVariable = 10
print("This variables are different:")
print(my_variable, My_variable, MyVariable)

# If you are using an expression in the right part of the assignment operator,
# the VALUE of the expression will be used:
c = 13-a+b*4
print("What value does c hold now? Let's have a look")
print(c)

# you can change the value of the variable:
a = 100
print("print variable a: ")
print(a)
a = "Ha-ha, I'm not a number anymore!"
print("print variable a: ")
print(a)

# 3. print() and input():
# As you have already seen, print() prints the VALUE of whatever
# is in the brackets.
# input() waits for you to type something, and then passes it on as a STRING.
# You need to assign that value to a variable otherwise it will disappear!

print("\nNow you type something!")
input() # nothing happened! Whatever you've typed is there no more.

print("Now type something again!")
a = input() # the line of text you've typed is now stored in the variable a
print("Let's see... Variable a now has the value: ")
print(a)

# You are now ready to write simple Q&A programs!
# try helloworld.py and questions.py