CHAPTER 5 — INPUT & OUTPUT - Printable Version

CHAPTER 5 — INPUT & OUTPUT - Printable Version

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CHAPTER 5 — INPUT & OUTPUT - Leejohnston - 11-15-2025

Chapter 5 — Input & Output
Your programs can now talk to the user

Up until now, your programs have only displayed information.

In this chapter, you will learn how to:
• ask the user for information
• store what they type
• respond to them
• create interactive programs

Input + output is the foundation of almost every real application.

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5.1 Output: print()

You already know print():

Code:
print("Hello!")

But now we go one step further.

Output becomes powerful when combined with input.

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5.2 Input: Asking the User Questions

To get information from the user, use:

Code:
input("Your question here: ")

Example:

Code:
name = input("What is your name? ")

print("Hello,", name)

If the user types:

Code:
Mia

The output is:

Code:
Hello, Mia

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5.3 Input Always Gives You a String

Important:

Whatever the user types comes in as TEXT (a string).

Example:

Code:
age = input("How old are you? ")

print(age + 1)    # ERROR!

Python sees “16” as text, not a number.

To convert to a number:

Code:
age = int(input("How old are you? "))

print(age + 1)

Now it works.

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5.4 Converting User Input

Use:
• int() → convert to whole number
• float() → convert to decimal
• str() → convert to text

Examples:

Code:
x = int(input("Enter a number: "))

y = float(input("Enter a decimal: "))

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5.5 Combining Input + Output

Try this:

Code:
name = input("What is your name? ")

food = input("What is your favourite food? ")

print("Nice to meet you,", name)

print("I also like", food)

Your program now behaves like a little conversation.

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5.6 A Simple Calculator Program

This program asks for two numbers and adds them:

Code:
a = float(input("Enter the first number: "))

b = float(input("Enter the second number: "))

total = a + b

print("The total is:", total)

This is your first interactive tool.

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5.7 Building a Custom Greeting

Try this:

Code:
name = input("Your name: ")

age = int(input("Your age: "))

print("Hello", name)

print("Next year you will be", age + 1)

This combines variables, input, and arithmetic.

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5.8 Avoiding Common Input Mistakes

Common mistake:

Code:
number = input("Enter a number: ")

print(number * 5)

If the user enters 3, the output is:

Code:
33333

Because Python repeats the string.

You MUST convert:

Code:
number = int(input("Enter a number: "))

print(number * 5)

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5.9 Exercise — Build a Personal Greeting App

Create a file called greet.py.

Ask the user for:
• their name
• their age
• their city

Then print a message like:

Code:
Hello Mia! You are 16 from Liverpool.

Try to format it neatly.

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5.10 Small Challenge

Make a program that asks the user for:
• a price
• a discount percentage

Then calculate the discounted price and display it.

Hint:

Code:
discount = price * (percent / 100)

final_price = price - discount

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5.11 Chapter Summary

• input() asks the user a question
• input ALWAYS returns a string
• use int() or float() to convert numbers
• combine input and output for interactive programs
• print() displays results and responses
• you can now build your first simple tools

Next:
Chapter 6 — Strings

This is where you learn how to manipulate text — a crucial skill for all beginners.

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Written and Compiled by Lee Johnston — Founder of The Lumin Archive