What Is a Function in Programming? A Simple Article for Beginners

Topic: basic programming knowledge
Audience: people who are new to programming
Level: beginner-friendly, minimal technical terms
Example language: Python
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1. What is a function?

In programming, a function is simply a group of instructions with a name.

Real-life example: you make tea every day. Making tea has several steps:

Instead of repeating all steps every time, we can give the whole task a name:

After that, when we say “make_tea,” we understand that there are several smaller steps inside.

Programming works in a similar way. We group several lines of code, give that group a name, and use the name when needed.

2. Why do we need functions?

Functions make code less repetitive, easier to read, and easier to fix.

Without a function:

print("Hello, An!")
print("Have a nice day!")

print("Hello, Binh!")
print("Have a nice day!")

print("Hello, Chi!")
print("Have a nice day!")

This works, but it repeats the same idea many times.

With a function:

def greet(name):
    print("Hello, " + name + "!")
    print("Have a nice day!")

greet("An")
greet("Binh")
greet("Chi")

Now the greeting is written only once. To greet someone, call greet() and put the person’s name inside.

3. Creating a simple function

In Python, a simple function looks like this:

def function_name():
    work_to_do

Example:

def say_hello():
    print("Hello!")

Simple explanation:

• def starts a function in Python.
• say_hello is the function name.
• The line below is what the function does.
• The code inside the function must be indented.

Creating a function does not run it immediately. To run it, you must call it:

def say_hello():
    print("Hello!")

say_hello()

Result:

4. What does calling a function mean?

Calling a function means asking it to start working.

Think of a button named “turn on the light.” Before you press it, the light is off. When you press it, the light turns on.

def turn_on_light():
    print("The light is on")

turn_on_light()

def turn_on_light() creates the button.
turn_on_light() presses the button.

Result:

5. A function can receive information

Many functions need information before they can work.

Example: greeting a person by name.

def greet(name):
    print("Hello, " + name + "!")

greet("An")
greet("Binh")

Result:

Here, name is a place to receive a name.

When we call:

greet("An")

Python understands that name is "An".

Simple way to think about it:

6. A function can return a result

Some functions only show text on the screen. Other functions calculate something and give the result back.

Example:

def add(a, b):
    return a + b

result = add(3, 5)

print(result)

Result:

Explanation:

• a receives 3.
• b receives 5.
• The function calculates 3 + 5.
• return gives the result back.
• result stores 8.

Simple meaning:

7. What is the difference between print and return?

Beginners often confuse these two.

print means show something on the screen.

return means give a result back to the program so it can use the result later.

Using print:

def add(a, b):
    print(a + b)

add(3, 5)

Displayed result:

Using return:

def add(a, b):
    return a + b

result = add(3, 5)
print(result * 2)

Result:

Because the function gives back 8, the program can use that result again.

Easy memory tip:

print = show it to the person.
return = give it back to the program.

8. Real example: calculating total price

def calculate_total(price, quantity):
    return price * quantity

total = calculate_total(25000, 3)

print(total)

Result:

Explanation:

• price is the price of one item.
• quantity is how many items are bought.
• The function multiplies price by quantity.
• The result is the total price.

To calculate other items:

print(calculate_total(10000, 5))
print(calculate_total(45000, 2))
print(calculate_total(120000, 1))

No need to write the same formula many times.

9. Real example: checking age

def check_age(age):
    if age >= 18:
        return "Adult"
    else:
        return "Not adult yet"

print(check_age(20))
print(check_age(15))

Result:

This function works like an age checker:

Put in an age.
If the age is 18 or more, return "Adult".
If the age is below 18, return "Not adult yet".

10. How to name a function

A function name should clearly say what the function does.

Unclear:

def x(a, b):
    return a + b

Clearer:

def add(a, b):
    return a + b

Beginner-friendly names:

greet_user()
add_numbers()
check_age()
calculate_total()
send_email()

For beginners, clear names are better than short names.

11. When should you create a function?

Create a function when:

• you write the same code many times;
• you want to name one clear task;
• you want code to be easier to read;
• you want to fix one place instead of many places;
• you want to split a big task into small tasks.

Instead of thinking:

Split it into smaller tasks:

Calculate total.
Calculate discount.
Print receipt.
Check stock.
Save customer information.

Each small task can become a function.

12. Common beginner mistakes

Mistake 1: Creating a function but not calling it

def say_hello():
    print("Hello!")

This does not print anything yet. You need to call the function:

say_hello()

Mistake 2: Forgetting indentation

Wrong:

def say_hello():
print("Hello!")

Correct:

def say_hello():
    print("Hello!")

Mistake 3: Confusing print and return

If you want to use the result later, use return.

def add(a, b):
    return a + b

If you only want to show something, use print.

def show_greeting():
    print("Hello!")

Mistake 4: Making one function do too many things

Do not make one function calculate money, send email, print a receipt, and save data all at once.

Use smaller functions:

calculate_total()
create_receipt()
send_email()
save_data()

One clear job per function is easier to understand.

13. How to read a function

When you see a function, ask:

1. What is the function name?
2. What does it receive?
3. What does it do?
4. Does it return a result?

Example:

def add(a, b):
    return a + b

Answers:

14. Small exercises

Exercise 1

Write a function named say_hello() that prints:

Exercise 2

Write a function named greet(name) that greets a person by name.

Example:

greet("An")

Result:

Exercise 3

Write a function named add(a, b) that returns the sum of two numbers.

Example:

print(add(4, 6))

Result:

Exercise 4

Write a function named calculate_total(price, quantity) that returns the total price.

Example:

print(calculate_total(20000, 3))

Result:

15. Suggested answers

Answer 1

def say_hello():
    print("Hello!")

say_hello()

Answer 2

def greet(name):
    print("Hello, " + name + "!")

greet("An")

Answer 3

def add(a, b):
    return a + b

print(add(4, 6))

Answer 4

def calculate_total(price, quantity):
    return price * quantity

print(calculate_total(20000, 3))

16. Quick memory notes

A function is a named group of instructions.

Creating a function prepares a task for reuse.

Calling a function makes it run.

A function can receive information.

A function can return a result with return.

print shows something to a person. return gives a result back to the program.

Function names should be clear and easy to understand.

17. What should you learn next?

After understanding functions, beginners can learn:

• how to split a small program into several functions;
• how to read errors when calling a function incorrectly;
• how to use lists together with functions;
• how to write a complete small program.

Do not rush. The key idea is simple: a function groups one task, gives that task a name, and lets you reuse it when needed.

References

1. Python Docs — Defining Functions: https://docs.python.org/3/tutorial/controlflow.html#defining-functions
2. MDN Web Docs — JavaScript Functions: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Functions
3. Harvard CS50’s Introduction to Programming with Python: https://cs50.harvard.edu/python/
4. Wikimedia Commons — programming image: https://commons.wikimedia.org/wiki/File:Colorful_code_(Unsplash).jpg