pycampaign02[variables].py

# 1. String Concatenation and Interpolation

# STRING INTERPOLATION:
# The process of evaluating a string literal containing one or more placeholders,yeilding a result 
# in which the placeholders are replaced with their corresponding values.

name="Shawki"
age=14
greeting="My name is "+name+". I am "+str(age)+" years old."
print(greeting) 
# this is not string interpolation. This is actually string cancatenation.
# but string cancatenation is too messy. 
# Moreover, here we can do mitakes and errors easily which is not good at all.

# so we can use string interpolation
name="Shawki"
age=14
greeting="My name is {}. I am {} years old.".format(name,age)
# here we are using placeholders(curly brackets) within the text ang replacing them with their values.
print(greeting) 
# this is much easier to read. We can read where the placeholders are.
# by using format method first value placed in the index of first placeholder and so on.
# but that is not necessary. we can just:
greeting="I am {age} years old. My name is {name}.".format(name=name,age=age)
print(greeting)
# or we can use placeholders index.
greeting="I am {1} years old. My name is {0}.".format(name,age)
print(greeting)
# so string interpolation is lot easier than cancatenation and it is error free too.
# it is pretty much a templete. this can be great use when we are riceiving values from database.
# again we can write our html code and we can put in this placeholders in web development.


# we can do that with "f" string too.
name="Shawki"
age=14
greeting=f"My name is {name}. I am {age} years old."
print(greeting) 





# 2. Variables

# The input function allows you to specify a massage to display and returns the value typed in by user.
# We use a variable to remember the value entered by the user.
# name = is a variable.
# here's variable name is "name". But we can call it anything as long the variable's name doesn't contain any space.
# if some one give new value in the previous variable, python will remember the last value.

# rules of variables-1.don't contain spaces.2.don't start with a number,3.the variable name should me specific because we can understand that easily.

# collect from the user-
name = input("what is your name?")
# display the value-
print(name)
#update the value-
name="mraha"
print(name)

# 2 ways for making newline in the input.
a=input("enter a number\n")

print("enter another number")
b=input()

# Working with variables-
firstname=input("what is your first name?\n")
lastname=input("what is your last name?\n")
print("hello,"+ firstname+lastname)

# Way to give spaces in the variables-
print("hello, "+firstname+""+lastname)
# use blank quotes between to variables in the string.

# swapping values between two variables
first =1
second=2

temp=first
first=second
second=temp

print(first)
print(second)

#or-
# shortest method
a=1
b=2

a,b=b,a  # magic line of code.
# this is is simultaneous assignment. it happens because automatic packing and unpacking data.

print(a)
print(b)

# we can also use multiple initialization at a single line.
a=b=c=d=e=20
# here a,b,c,d,e all are alias of each other.