Lesson 8 of 12

Functions: name a job, use it again

Learn functions with flowchart blocks: give a job a name, Call it with values, and Return the answer. Open working examples and see them as real code.

About 6 minutes · 3 parts, each with a program to try

Part 1 of 3

A function is a flowchart of its own

A Function block starts a small flowchart with a name, like discount, and the values it's given, like price.

Write a job once, then use it as often as you like.

Example · FunctionsPrice MachineBuild a lineTotal(price, qty) function once, then use it for pens and for notebooks.

Try it

1def lineTotal(price, qty):2    cost = price * qty3    return cost4
5
6print("Stationery shop: pens ₹10 each, notebooks ₹45 each")7pens = int(input("How many pens? "))8pensCost = lineTotal(10, pens)9books = int(input("How many notebooks? "))10booksCost = lineTotal(45, books)11total = pensCost + booksCost12print("Pens: ₹" + str(pensCost))13print("Notebooks: ₹" + str(booksCost))14print("Total to pay: ₹" + str(total))

Part 2 of 3

Call it, and Return the answer

A Call block runs the function with real values, like discount(500). Its Return block gives the answer back, and the Call keeps it in a value.

Press Step and watch the program jump into the function and back.

Example · FunctionsGrade FunctionA gradeFor(mark) function with a Return on each path, called for every mark in a list.

Try it

1def gradeFor(score):2    if score >= 80:3        return "A"4    elif score >= 60:5        return "B"6    elif score >= 40:7        return "C"8    else:9        return "Fail"10
11
12marks = [92, 67, 48, 30]13for mark in marks:14    grade = gradeFor(mark)15    print("Mark " + str(mark) + " is grade " + grade)16print("All marks graded!")

Part 3 of 3

A function that calls itself

A function can Call itself, with a smaller problem each time: fact(5) is 5 * fact(4). That's recursion.

It needs a stop (the base case), like n <= 1. Open Values and Step: each call waits on the call stack until the one above it gives back its answer.

Example · RecursionFactorial (Recursion)A fact(n) function that calls itself: fact(5) waits for fact(4), down to fact(1). Open Values and Step to watch the call stack.

Try it

1def fact(n):2    if n <= 1:3        return 14    else:5        smaller = fact(n - 1)6        return n * smaller7
8
9n = int(input("Factorial of which number? "))10answer = fact(n)11print(str(n) + "! = " + str(answer))

Blocks in this lesson

Function Call Return

Quick check

What does a Return block do?

Practise this

World 5 challengesBuild it yourself, with three hints each.🛒 Supermarket TrolleyA Story Mode story that uses it.