How do you find the term X in the Fibonacci sequence?

Question

I have to do a C# program that gets a number X which will be the term of the sequence and print it on the screen.

Answer 1

I was going to answer "calculating each term as far as you want". I was already thinking about making a recursive and a repetitive solution. But then I came up with the idea of looking for a better solution. And I found this in that reply in the OS (and solved by the more traditional forms as well):

using static System.Console;
using static System.Math;
                    
public class Program {
    public static void Main() {
        for (int i = 0; i < 20; i++) WriteLine($"{Fib(i)}, {FibIte(i)}, {FibRec(i)}");
    }
    static int Fib(int n) {
        double sqrt5 = Sqrt(5);
        double p1 = (1 + sqrt5) / 2;
        double p2 = -1 * (p1 - 1);
        return (int)((Pow(p1, n) - Pow(p2, n)) / sqrt5);
    }
    static int FibIte(int n) {
        int a = 0;
        int b = 1;
        for (int i = 0; i < n; i++) {
            int temp = a;
            a = b;
            b = temp + b;
        }
        return a;
    }
    static int FibRec(int n) => n < 2 ? n : FibRec(n - 1) + FibRec(n - 2);
}

Behold working in the ideone. And in the .NET Fiddle. Also put on the Github for future reference.