Я бы сделал это так:
1. Get a number
2. While the user is not hitting the right number:
2.1 let the user know if the number was too big or too small
2.2 ask for another number
2.3 count number-of-attems + 1
3. If the user arrived here, it means it has the number right, print number-of-attems
В коде это может выглядеть так:
public static void Main(string[] args)
{
Console.WriteLine("The secret number\n");
Random randomerare = new Random();
int slump_tal = randomerare.Next(1, 101);
Console.WriteLine("Write your number and we'll see where it lands:\n");
Console.WriteLine();
int user_nr = Convert.ToInt32(Console.ReadLine());
// Here you can store the attempts
int attempts = 1;
// While the user provides the wrong answer, we iterate
while(slump_tal != user_nr)
{
// We add 1 to the counter
attempts++;
if (slump_tal > slump_tal)
{
Console.WriteLine("Wrong Your number is too low!\n");
}
else
{
Console.WriteLine("Wrong! Your number is too big!\n");
}
user_nr = Convert.ToInt32(Console.ReadLine());
}
Console.WriteLine($"Bravo! That's the correct number. you did it in {attempts} attemps");
Console.WriteLine("The secret number was: {0}\n\nPush the button to finish", slump_tal);
Console.ReadKey(true);
}