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Go Practice Exercises

Fibonacci Sequence in Go

Build the Fibonacci numbers with a loop, a double assignment and a slice.

  • Beginner
  • 2 min read
  • 1 runnable example
What you'll learn
  • A loop with two variables
  • a, b = b, a+b
  • Why uint64
Run code →
The first numbers
00
11
12
23
34
55
5 = 2 + 3

Each number is the sum of the two before

Each Fibonacci number is the sum of the two before it, starting from 0 and 1. Build the first numbers of the sequence in a slice.

a and b hold two neighbouring numbers. a, b = b, a+b moves both one step forward in a single assignment. uint64 is used because Fibonacci numbers grow quickly: the 50th no longer fits in 32 bits.

Key points

  1. Start from 0 and 1.
  2. One assignment moves both values.
  3. uint64 holds much larger numbers than int32.

Runnable Go example

Go
Run code →
main.go
package main

import "fmt"

func fibonacci(count int) []uint64 {
	sequence := make([]uint64, 0, count)
	a, b := uint64(0), uint64(1)
	for i := 0; i < count; i++ {
		sequence = append(sequence, a)
		a, b = b, a+b
	}
	return sequence
}

func main() {
	fmt.Println(fibonacci(10))
	fmt.Println("50th:", fibonacci(50)[49])
}
Get a Run button for this example Result of running the code
[0 1 1 2 3 5 8 13 21 34]
50th: 7778742049

Practice

Open the example in the online compiler, change a value or add a line, and predict the output before you run it. Then break the code on purpose and read the compiler's message.

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