How can I validate console input as integers?

Question

I have written my codes and i want to validate it in such a way thet it will only allow intergers to be inputed and not alphabets. Here is the code, please I will love you to help me. Thanks.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace minimum
{
    class Program
    {
        static void Main(string[] args)
        {
            int a = Convert.ToInt32(Console.ReadLine());
            int b = Convert.ToInt32(Console.ReadLine());
            int c = Convert.ToInt32(Console.ReadLine());

            if (a < b)
            {
                if (a < c)
                {
                    Console.WriteLine(a + "is the minimum number");
                }
            }
            if (b < a)
            {
                if (b < c)
                {
                    Console.WriteLine(b + "is the minimum number");
                }
            }
            if (c < a)
            {
                if (c < b)
                {
                    Console.WriteLine(c + "is the minimum number");
                }
            }


            Console.ReadLine();
        }
    }
}

Answer 1

You should test if it's an int instead of converting in right away. Try something like :

string line = Console.ReadLine();
int value;
if (int.TryParse(line, out value))
{
   // this is an int
   // do you minimum number check here
}
else
{
   // this is not an int
}

Answer 2

To get the console to filter out alphabetical keystrokes you have to take over input parsing. The Console.ReadKey() method is fundamental to this, it lets you sniff the pressed key. Here's a sample implementation:

    static string ReadNumber() {
        var buf = new StringBuilder();
        for (; ; ) {
            var key = Console.ReadKey(true);
            if (key.Key == ConsoleKey.Enter && buf.Length > 0) {
                return buf.ToString() ;
            }
            else if (key.Key == ConsoleKey.Backspace && buf.Length > 0) {
                buf.Remove(buf.Length-1, 1);
                Console.Write("\b \b");
            }
            else if ("0123456789.-".Contains(key.KeyChar)) {
                buf.Append(key.KeyChar);
                Console.Write(key.KeyChar);
            }
            else {
                Console.Beep();
            }
        }
    }

You could add, say, Decimal.TryParse() in the if() statement that detects the Enter key to verify that the entered string is still a valid number. That way you can reject input like "1-2".