Recap - Factorial

Part of the Fundamentals section of Coddy's Swift journey — lesson 47 of 86.

Time to put your loop skills to the test! The factorial is a classic programming problem that's perfect for practicing loops.

A factorial of a number n (written as n!) is the product of all positive integers from 1 to n. For example:

5! = 5 × 4 × 3 × 2 × 1 = 120
3! = 3 × 2 × 1 = 6
1! = 1

To calculate a factorial with a loop, you start with a result of 1 and multiply it by each number in the range:

var result = 1
let n = 5

for i in 1...n {
    result *= i
}
print(result)  // Output: 120

The loop multiplies result by 1, then 2, then 3, and so on until it reaches n. Each iteration builds on the previous result.

Challenge

Easy

Write a function factorial that takes n and returns the factorial of that number.

Use a loop to multiply all positive integers from 1 to n together.

Parameters:

n (Int): A positive integer (1 or greater)

Returns: The factorial of n (Int)

For example, if n is 4, the function calculates 1 × 2 × 3 × 4 = 24 and returns 24.

Cheat sheet

A factorial of a number n (written as n!) is the product of all positive integers from 1 to n:

5! = 5 × 4 × 3 × 2 × 1 = 120
3! = 3 × 2 × 1 = 6
1! = 1

To calculate a factorial with a loop, start with a result of 1 and multiply it by each number in the range:

var result = 1
let n = 5

for i in 1...n {
    result *= i
}
print(result)  // Output: 120

Try it yourself

func factorial(n: Int) -> Int {
    // Write code here
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Fundamentals

1Introduction

The Language Hello World!Comments

4Operators Part 1

Arithmetic Operators Modulo Operator Compound Assignment Recap - Simple Math Comparison Operators

7Basic IO

Print Function String Interpolation ReadLine Input Type Conversion Recap - Till 120 Recap - True or False

10Functions

Declare A Function Parameters And Arguments Return Values Argument Labels Recap - Sigma Function Recap - Validation Function Default Values

13Iterating Over Sequences

Iterating Over Elements The Enumerated Method Iterating Over Strings P1 Iterating Over Strings P2

16Final Challenges

Flat Asterisk Pyramid Pattern Finder What To Buy

2Variables

Let vs Var Type Annotations Numbers String Boolean Naming Conventions Recap - Initialize Variables

5Operators Part 2

Logical Operators Part 1 Logical Operators Part 2 Recap - Simple Logic Logical Operators Part 3 Ternary Operator

8Bill Split Calculator

Welcome Message Getting Input

Calculating Tip And Total

Splitting The Bill

Formatted Output

11FizzBuzz with a Twist

Game Overview The FizzBuzz Function

Looping The Numbers

Adding The Twist

14Arrays Advanced

Array Slicing Part 1 Array Slicing Part 2 Sequence Operators The Contains Method

3Optionals

What Are Optionals Unwrapping With If Let Guard Let Nil Coalescing Operator Recap - Safe Unwrapping

6Decision Making

If Statement If - Else Recap - Simple Calculator Switch Statement Switch With Ranges

9Loops

For-In Loop While Loop Repeat-While Loop Break ContinueRecap - FactorialRanges In Loops Nested Loop Recap - Dynamic Input

12Arrays Basics

Declaring An Array Accessing Elements Modifying Arrays Array Methods Recap - Product List Recap - Reversed Array Tuples

15Daily Expense Tracker

Project Overview Exit The Program