Swap.cs

using System;

namespace IntSwap
{
    class Program
    {
        static void Main(string[] args)
        {
            int i = 1, j = 2;
            Swap1(ref i, ref j);
            Console.WriteLine($"i = {i}, j = {j}");

            Swap2(ref i, ref j);
            Console.WriteLine($"i = {i}, j = {j}");

            int? nullI = 1, nullJ = 2;
            Swap3(nullI, nullJ);
            Console.WriteLine($" nullI  = { nullI },  nullJ  = { nullJ }");
            /*OUTPUT:
            i = 2, j = 1
            i = 1, j = 2
            nullI  = 1,  nullJ  = 2*/
        }

        public static void Swap1(ref int a, ref int b)
        {
            var temp = a;
            a = b;
            b = temp;
        }

        public static void Swap2(ref int a, ref int b) => (a, b) = (b, a);

        public static void Swap3(int? a, int? b)
        {
            var temp = a;
            a = b;
            b = temp;
        }
    }
}