“Calculator Functions” or “Temperature Converter”
24 minutes read
Beginner friendly
Includes practice
Hi there! 👋 In this lesson, you’ll write small, reusable functions to add calculator features, convert temperatures between Celsius and Fahrenheit.
By the end, you should be able to:
- Explain what a function is, why we wrap code in a function, and how to call one
- Write your own functions using
def, parameters, andreturn - Combine simple functions to build a slightly bigger program
Take it step-by-step, run the examples, and try the practice before peeking ahead. You’ve got this!
Runtic's Learning Tips
Think of functions as reusable tools — once you build them correctly, you can use them anywhere in your code
Test each function by calling it with inputs and checking the output immediately
Functions help break problems into smaller chunks — don’t try to solve everything at once
Why Use Functions?
Imagine copying the same 3 lines every time you want to add two numbers — sounds repetitive and error-prone, right? That’s where a function comes in handy.
We can:
- Give the task a name (
add) - Hide the details inside the function body
- Reuse it with a short call anywhere
This keeps your code clean and efficient.
Quick Summary
Functions group related logic into a reusable component
They reduce repetition and allow for easier debugging
Defining a function makes code neater and more readable
Calculator Functions – Core Examples
Interactive Code EditorExample Code
pythonThis won’t affect your saved progress.
Notice:
defintroduces the function with name and input parameters- Inside, the
returnkeyword sends back a value - Once defined, we can call the function just like
print()orlen()
Quick Practice
2 minutesCheck what you understand about how return and parameter work in functions.
What does the return keyword do?
What happens if you don’t write return in a function?
Practice: Add multiply() and divide()
Practice Challenge
Write two functions: multiply(a,b)that returns the product of two numbers, and divide(a,b)that returns the result of dividing aby b.If bis 0, return "Error".Then call both functions with 5 and 3 (for multiply) and 5 and 2 (for divide). Finally, print both results to verify.
Use * for multiplication and / for division. Handle divide-by-zero carefully.
A Menu-Driven Calculator Function
By building small functions, we can plug them into a larger “menu” system:
Practice Challenge
Complete the functions for add,subtract,multiply,divide,and implement calculator(a,b,operator)that uses them. Handle divide-by-zero and unknown operators. Then test it with multiple operators and store each outcome in separate result variables (result,result2,result3,result4).
Implement calculator(a, b, operator) that performs addition, subtraction, multiplication, and division using helper functions.
Quick Practice
3 minutesMore quiz-style checks to boost recall before moving on.
True or False: A function MUST take at least one parameter.
What keyword immediately exits a function and hands back a result?
What error will calling multiply(4) (with one input) trigger?
Temperature Converter – Reuse More Logic
Interactive Code EditorExample Code
pythonThis won’t affect your saved progress.
Math Recap:
- °C to °F = multiply by 9/5, then add 32
- °F to °C = subtract 32, then multiply by 5/9
Practice: Add Kelvin Support
Practice Challenge
Define two functions: c_to_k(c)and k_to_c(k)to convert between Celsius and Kelvin using the formulas Kelvin=Celsius+273.15and Celsius=Kelvin-273.15.Then create variables cand k,call the functions, and print the results rounded to two decimal places.
Use Kelvin = Celsius + 273.15 and Celsius = Kelvin - 273.15. Round the results for clean output.
- Defined and used functions to return answers like add/subtract
- Saw how functions let us reuse and build onto clean logic
- Wrote practical temperature + calculator tools using functions
- Practiced quick checks to boost long-term memory
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