Day 10 – Taking User Input in Python

Welcome to Day 10 of 100 Days of Python!

Until now, most of our programs have worked with values that we directly wrote inside the code.

But what if we want the user to provide the data while the program is running?

That's where Python's built-in input() function comes in.

In this lesson, we will learn:

• How to take input from a user

• How input() works

• Why input() always returns a string

• How to take integer and float input

• How to use a prompt with input()

• How type casting works with user input

• A common mistake when performing calculations with input

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1. What is User Input?

User input is data provided by a user while a program is running.

Python provides the built-in input() function to take input from the user.

The basic syntax is:

variable = input()

For example:

name = input()

print(name)

If the user enters:

Sritesh

The output will be:

Sritesh

The value entered by the user is stored in the variable name.

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2. How Does input() Work?

When Python encounters input(), the program pauses and waits for the user to enter something.

For example:

name = input()

print("Hello, " + name)

If the user enters:

Sritesh

The program produces:

Hello, Sritesh

So the basic flow is:

Program
   ↓
input()
   ↓
User enters data
   ↓
Python receives the data
   ↓
Value is stored in a variable

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3. Important: input() Always Returns a String

This is one of the most important things to remember about input():

The input() function always returns the user's input as a string (str).

For example:

age = input()

print(age)
print(type(age))

If the user enters:

23

The output will be:

23
<class 'str'>

Even though we entered 23, Python received it as:

"23"

not:

23

This becomes very important when we want to perform calculations.

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4. Taking Integer Input

If we need an integer from the user, we can use int() with input().

age = int(input())

print(age)
print(type(age))

If the user enters:

23

Output:

23
<class 'int'>

Here:

input()

takes the input as a string, and:

int()

converts that string into an integer.

The process is:

User enters 23
      ↓
input()
      ↓
"23"
      ↓
int()
      ↓
23

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5. Taking Float Input

We can also take decimal values using float().

price = float(input())

print(price)
print(type(price))

If the user enters:

99.50

Output:

99.5
<class 'float'>

The general pattern is:

integer_value = int(input())
float_value = float(input())
string_value = input()

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6. Displaying a Message with input()

We don't have to leave input() empty.

We can provide a message inside the parentheses.

This message is called the prompt.

Example:

name = input("Enter your name: ")

print(name)

The user will see:

Enter your name: Sritesh

After entering the name, the program prints:

Sritesh

The syntax is:

variable = input("Prompt message")

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7. Creating a Greeting Program

We can combine input() with string concatenation to create a simple interactive program.

name = input("Enter your name: ")

print("Hello, " + name + "!")

Example:

Enter your name: Sritesh
Hello, Sritesh!

This is more useful than hard-coding the name:

print("Hello, Sritesh!")

because now the program can greet different users.

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8. Taking Multiple Inputs

We can take multiple values from the user and store them in different variables.

For example:

first_name = input("Enter your first name: ")
last_name = input("Enter your last name: ")

print("Hello,", first_name, last_name)

Example:

Enter your first name: Sritesh
Enter your last name: Suranjan
Hello, Sritesh Suranjan

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9. A Common Mistake with Numbers

Consider this program:

a = input("Enter first number: ")
b = input("Enter second number: ")

print(a + b)

Suppose the user enters:

10
20

You might expect:

30

But the output is:

1020

Why?

Because input() returns strings.

Python is actually performing:

"10" + "20"

For strings, + means concatenation, not mathematical addition.

So:

"10" + "20"
      ↓
"1020"

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10. Converting User Input to Integers

To perform numerical addition, we need to convert the input into integers.

a = input("Enter first number: ")
b = input("Enter second number: ")

print(int(a) + int(b))

If the user enters:

10
20

The output is:

30

We can also convert the values while taking the input:

a = int(input("Enter first number: "))
b = int(input("Enter second number: "))

print(a + b)

This is a very common pattern in Python.

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11. Practical Example

Let's combine everything we have learned so far.

name = input("Enter your Name: ")
print("Hello, " + name + "!")

first_number = input("Enter first number: ")
second_number = input("Enter second number: ")

print(first_number + second_number)
print(int(first_number) + int(second_number))

Example:

Enter your Name: Sritesh
Hello, Sritesh!
Enter first number: 10
Enter second number: 20
1020
30

The first result:

1020

is string concatenation.

The second result:

30

is numerical addition after type conversion.

This example connects directly with what we learned on Day 9 – Type Casting in Python.

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12. input() with Different Data Types

Here are some common patterns:

String

name = input("Enter your name: ")

Integer

age = int(input("Enter your age: "))

Float

price = float(input("Enter the price: "))

Remember:

input()

itself always produces a string.

The conversion happens because we explicitly use:

int()

or:

float()

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13. Complete Program

Here is the complete program for today's lesson:

a = input("Enter your Name: ")
print("Hello, " + a + "!")

b = input("Enter first number: ")
c = input("Enter second number: ")

print(b + c)
print(int(b) + int(c))

Example output:

Enter your Name: Sritesh
Hello, Sritesh!
Enter first number: 10
Enter second number: 20
1020
30

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14. Important Things to Remember

input() always returns a string

value = input()
print(type(value))

Output:

<class 'str'>

Use int() for integers

age = int(input())

Use float() for decimal numbers

price = float(input())

Use a prompt to guide the user

name = input("Enter your name: ")

Don't forget type conversion for calculations

a = int(input())
b = int(input())

print(a + b)

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15. Quick Revision

                User Input
                    │
                    ▼
                 input()
                    │
                    ▼
              Always returns
                 a string
                    │
          ┌─────────┴─────────┐
          ▼                   ▼
       int()                float()
          │                   │
          ▼                   ▼
       Integer              Float

Remember These:

name = input("Enter your name: ")

age = int(input("Enter your age: "))

price = float(input("Enter the price: "))

And remember the classic beginner example:

"10" + "20"           # "1020"

int("10") + int("20") # 30

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16. Key Takeaways

After completing Day 10, you should understand:

• What user input is

• How to use Python's input() function

• How to store user input in variables

• Why input() always returns a string

• How to take integer input using int()

• How to take decimal input using float()

• How to display a prompt to the user

• Why "10" + "20" produces "1020"

• How type casting allows us to perform numerical calculations

• How to create a simple interactive Python program

The input() function is an important step because our programs are no longer limited to values written directly in the source code. We can now make programs that interact with users and respond to the data they provide.

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📂 Day 10 Resources

All notes and code for this day are available in the GitHub repository:

https://github.com/SriteshSuranjan/100-Days-of-Python/tree/main/10-Day10-Taking-User-Input

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