int c;
string message;
int count;
bool res;

Console.WriteLine("Please, enter an integer.");
message = Console.ReadLine();
res = int.TryParse(message, out c);
count = 0; // The user has 3 tries: count will be 0, 1, 2, and then we default.
while (!res && count < 3)
{
    count++;
    if (count == 3)
        {
        c = 1;
        Console.WriteLine("I'm using the default value 1.");
        }
    else
        {
        Console.WriteLine("The value entered was not an integer.");
        Console.WriteLine("Please, enter an integer.");
        message = Console.ReadLine();
        res = int.TryParse(message, out c);
        }
}
Console.WriteLine("The value is: " + c);

do
{
    <statement block>
} while (<condition>);

        int age;
        string answer;

        do
        {
            Console.Write("Please, enter your age.\n");
            answer = Console.ReadLine();
        } while (! int.TryParse(answer, out age) || age < 0);

using System;

class Loan
{
    private string account;
    private char type;
    private int cscore;
    private decimal amount;
    private decimal rate;

    public Loan()
    {
        account = "Unknown";
        type = 'o';
        cscore = -1;
        amount = -1;
        rate = -1;
    }

    public Loan(string nameP, char typeP, int cscoreP, decimal needP, decimal downP)
    {
        account = nameP;
        type = typeP;
        cscore = cscoreP;
        if (cscore < 300)
        {
            Console.WriteLine("Sorry, we can't accept your application");
            amount = -1;
            rate = -1;
        }
        else
        {
            amount = needP - downP;

            switch (type)
            {
                case ('a'):
                    rate = .05M;
                    break;

                case ('h'):
                    if (cscore > 600 && amount < 1000000M)
                        rate = .03M;
                    else
                        rate = .04M;
                    break;
                case ('o'):
                    if (cscore > 650 || amount < 10000M)
                        rate = .07M;
                    else
                        rate = .09M;
                    break;

            }

        }
    }
    public override string ToString()
    {
        string typeName = "";
        switch (type)
        {
            case ('a'):
                typeName = "an auto";
                break;

            case ('h'):
                typeName = "a house";
                break;
            case ('o'):
                typeName = "another reason";
                break;

        }

        return "Dear " + account + $", you borrowed {amount:C} at {rate:P} for "
            + typeName + ".";
    }
}

using System;
class Program
{
    static void Main()
    {

        Console.WriteLine("What is your name?");
        string name = Console.ReadLine();

        Console.WriteLine("Do you want a loan for an Auto (A, a), a House (H, h), or for some Other (O, o) reason?");
        char type = Console.ReadKey().KeyChar; ;
        Console.WriteLine();

        string typeOfLoan;

        if (type == 'A' || type == 'a')
        {
            type = 'a';
            typeOfLoan = "an auto";
        }
        else if (type == 'H' || type == 'h')
        {
            type = 'h';
            typeOfLoan = "a house";
        }
        else
        {
            type = 'o';
            typeOfLoan = "some other reason";
        }

        Console.WriteLine($"You need money for {typeOfLoan}, great.\nWhat is your current credit score?");
        int cscore = int.Parse(Console.ReadLine());

        Console.WriteLine("How much do you need, total?");
        decimal need = decimal.Parse(Console.ReadLine());

        Console.WriteLine("What is your down paiement?");
        decimal down = decimal.Parse(Console.ReadLine());

        Loan myLoan = new Loan(name, type, cscore, need, down);
        Console.WriteLine(myLoan);
    }

}