Recursion

This Go program demonstrates a simple factorial function and a recursive Fibonacci function.

// Importing the "fmt" package, which provides functions for formatted I/O.
import "fmt"

// Function fact calculates the factorial of an integer using recursion.
func fact(n int) int {
    // Base case: factorial of 0 is 1.
    if n == 0 {
        return 1
    }

    // Recursive case: n! = n * (n-1)!
    return n * fact(n-1)
}

// The main function, which serves as the entry point for the program.
func main() {
    // Printing the factorial of 7 using the fact function.
    fmt.Println(fact(7))

    // Declaring a variable fib as a function type that takes an integer parameter and returns an integer.
    var fib func(n int) int

    // Assigning a recursive anonymous function to the fib variable.
    fib = func(n int) int {
        // Base cases: Fibonacci of 0 is 0, and Fibonacci of 1 is 1.
        if n < 2 {
            return n
        }

        // Recursive case: fib(n) = fib(n-1) + fib(n-2)
        return fib(n-1) + fib(n-2)
    }

    // Printing the 7th Fibonacci number using the fib function.
    fmt.Println(fib(7))
}

Output

040
13

Now, let's break down the code and explain each part:

1. Function Declarations:

   • fact(n int) int: This function calculates the factorial of an integer n using recursion.

2. Main Function:

   • main(): This is the entry point of the program.

   • fmt.Println(fact(7)): Calls the fact function and prints the factorial of 7.

   • Declares a variable fib as a function type that takes an integer parameter and returns an integer.

   • fib = func(n int) int { ... }: Assigns a recursive anonymous function to the fib variable.

   • fmt.Println(fib(7)): Calls the fib function and prints the 7th Fibonacci number.