P4- Variables and Data Types.md

Here's a Python program to print a little story using 'print()' function.

print("There was a man named Saurabh who was 30 years old")
print("He liked his name Saurabh")
print("But hated to be 30 years old")

Suppose, we wanted to change the name and age of the person. We would have to go change the required data wherever it appears. It's where the importance of variables arises. A variable is a container which can store a particular data. If we change the data in a variable, data changes wherever that variable occurs reducing unnecessay hard work.

Syntax-

variable_name = data

Now, the type of data we store in a variable specifies the data type of a variable. A data type of a variable is the type of data stored by a variable. Some most used data types are-

1. String(str) - A string of characters

a = "Python is a programming language"

A string is always declared with double quotes.

2. Integer(int) - An integer number

a = 10

3. Float(float) - A decimal number

a = 1.5

4. Double Float(double) - A decimal number with more significant digits.

a = 1.4998

5. Boolean(bool) - Boolean True or False

a = True

There's a great difference between a = 10 and a = "10". While the former is an integer, the latter is a string. Mathematical operations can't be performed on a string.

If you recall our first program, to print a string, we wrote the following code.

print("Hello World!")

What we did here is printing a string. Another way to accomplish this is by using a variable. A variable can be printed as print(variable_name) which prints the value of the variable.

# A program to print 'Hello world!'
string  = "Hello World!"
print(string)

Output-

Hello World!

If we want to use a string along with a variable, we may do as in the following program.

# A python program to show concepts of variables
color = "Red"
number = 7
print("My favourite color is " + color)  # concatenating two strings
print("My favourite number is " + str(number))  # converting an integer into a string to concatenate

Output-

My favourite color is Red
My favourite number is 7

Explanation-

In the first print statement, string 'color' has been concatenated with another string ' "My favourite color" '. In the second print statement, we were trying to concatenate a string with an integer, which is not possible and will produce an error. To remove such an error, we'll have to convert the integer into a string as 'str(var_name).

Concatenation of string is combining of two or more strings with each other. To read more about concatenation of strings, click here.

Coming back to our story, using the above concepts we can change our code as follows.

name = "Saurabh"
age = "30"
print("There was a man named" + name + " who was " + age + " years old")
print("He liked his name " + name)
print("But hated to be " + age + " years old")

Output-

There was a man named Saurabh who was 30 years old
He liked his name Saurabh
But hated to be 30 years old

Now, if we want to edit the name in the story, we can do that by just editing the name in the variable name.