Program.cs

using System;
using NBitcoin;
// ReSharper disable All

namespace BitcoinAddress
{
    class Program
    {
        static void Main()
        {
            Key privateKey = new Key(); // generate a random private key
            var mainNetPrivateKey = privateKey.GetBitcoinSecret(Network.Main);  // get our private key for the mainnet
            var testNetPrivateKey = privateKey.GetBitcoinSecret(Network.TestNet);  // get our private key for the testnet
            Console.WriteLine(mainNetPrivateKey); // L5B67zvrndS5c71EjkrTJZ99UaoVbMUAK58GKdQUfYCpAa6jypvn
            Console.WriteLine(testNetPrivateKey); // cVY5auviDh8LmYUW8AfafseD6p6uFoZrP7GjS3rzAerpRKE9Wmuz

            Console.ReadLine();
        }
    }
}