In this tutorial, we will learn how to generate a Fibonacci series up to a given number in Swift. We will understand what the Fibonacci series is, write an algorithm to generate it, and implement the algorithm step by step with a complete Swift program and output.

What is the Fibonacci Series?

The Fibonacci series is a sequence of numbers where each number is the sum of the two preceding ones, starting from 0 and 1. The sequence goes: 0, 1, 1, 2, 3, 5, 8, 13, 21...

The Fibonacci series is widely used in mathematics, computer science, and even nature to describe patterns such as spirals in shells and trees.

Algorithm to Generate Fibonacci Series

To generate a Fibonacci series up to a given number n, follow these steps:

  1. Start with two initial numbers: a = 0 and b = 1.
  2. Print the value of a.
  3. Calculate the next number in the series as c = a + b.
  4. Update a to b and b to c.
  5. Repeat the process until the value of a exceeds the given number n.

This algorithm is straightforward and ensures that all Fibonacci numbers less than or equal to n are printed.

Step-by-Step Implementation in Swift

Let’s implement the algorithm in Swift step by step.

1. Define the Function

Create a function generateFibonacci that accepts the maximum number n as a parameter and prints the Fibonacci series:

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func generateFibonacci(upTo n: Int) {
    var a = 0   // First Fibonacci number
    var b = 1   // Second Fibonacci number
    
    while a <= n {
        print(a, terminator: " ")  // Print the current number
        let c = a + b              // Calculate the next number
        a = b                      // Update a to b
        b = c                      // Update b to the new value
    }
    print() // Move to the next line after printing the series
}

Explanation:

var a = 0: Initializes the first Fibonacci number.

var b = 1: Initializes the second Fibonacci number.

while a <= n: Ensures that the series stops once the value of a exceeds n.

print(a, terminator: " "): Prints the current number without moving to the next line.

let c = a + b: Calculates the next Fibonacci number.

a = b and b = c: Updates the variables for the next iteration.

2. Test the Function

Let’s test the function by generating Fibonacci series for different values of n:

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// Test cases
print("Fibonacci series up to 10:")
generateFibonacci(upTo: 10)

print("Fibonacci series up to 50:")
generateFibonacci(upTo: 50)

print("Fibonacci series up to 100:")
generateFibonacci(upTo: 100)

Each test case calls the function with a different maximum value, generating the corresponding Fibonacci series.

Complete Swift Program

Here’s the complete Swift program that generates Fibonacci series up to a given number:

main.swift

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import Foundation

// Function to generate Fibonacci series up to a given number
func generateFibonacci(upTo n: Int) {
    var a = 0   // First Fibonacci number
    var b = 1   // Second Fibonacci number
    
    while a <= n {
        print(a, terminator: " ")  // Print the current number
        let c = a + b              // Calculate the next number
        a = b                      // Update a to b
        b = c                      // Update b to the new value
    }
    print() // Move to the next line after printing the series
}

// Test cases
print("Fibonacci series up to 10:")
generateFibonacci(upTo: 10)

print("Fibonacci series up to 50:")
generateFibonacci(upTo: 50)

print("Fibonacci series up to 100:")
generateFibonacci(upTo: 100)

Output

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Fibonacci series up to 10:
0 1 1 2 3 5 8 
Fibonacci series up to 50:
0 1 1 2 3 5 8 13 21 34 
Fibonacci series up to 100:
0 1 1 2 3 5 8 13 21 34 55 89 
Program ended with exit code: 0

Screenshot from Xcode