Accept only numbers in the C#console app

Question

Good evening, I’m trying to get the Console.Readline() command to read only numbers, ignoring characters, there’s a way ?

example:

static void main()
{
    int x;

    Console.WriteLine("INSERINDO VALOR PARA X");

    x=int.Parse(Console.ReadLine()) //em execução quero que o console só aceite números inteiros do teclado.

}

Answer 1

Gabriel, if there’s any native way to do this, I’m sorry but I don’t know.

Generally, people adopt a loop that keeps the user "stuck" while what they type is not a number, and the cast is done in a way that does not create an exception.

Take an example:

using System;

class ReadLineInt {
  static void Main() {
    int x;

    Console.WriteLine("INSERINDO VALOR PARA X");

    while(!int.TryParse(Console.ReadLine(), out x)) {
         Console.WriteLine("Insira apenas números inteiros");
         Console.WriteLine("INSERINDO VALOR PARA X");
    }

    Console.WriteLine("Número digitado: " + x);
  }
}

Answer 2

You can implement a method that reads exclusively numbers pressed within the Console. For this you will have to start a loop and have to test each iteration if a key was pressed with Console.KeyAvailable which returns a boolean indicating if there has been the pressing of a key.

If Console.KeyAvailable To charge a keystroke is to instruct the reading of the key with Console.ReadKey(); passing by true as the first parameter to prevent the read key from being printed on the 'Console' screen'.

Then test the nature of the pressed key:

• If it’s a number accumulate in the string return method.

• If the enter key ends the iteration.

• If the back space key removes the last character from the console (see code settings).

• Any other value ignore.

Using switch case when with the syntax of version 7 or higher of C#:

using System;

class Exemplo
{
    public static string lerNumeros()
    {
        ConsoleKeyInfo cki;
        string entrada = "";
        bool continuarLoop = true;
        while (continuarLoop)
            if (Console.KeyAvailable)
            {
                cki = Console.ReadKey(true);
                switch (cki.Key)
                {
                    case ConsoleKey.Backspace:
                        if (entrada.Length == 0) continue;
                        entrada = entrada.Remove(entrada.Length - 1);
                        Console.Write("\b \b"); //Remove o último caractere digitado
                        break;
                    case ConsoleKey.Enter:
                        continuarLoop = false;
                        break;
                    case ConsoleKey key when ((ConsoleKey.D0 <= key) && (key <= ConsoleKey.D9) ||                       
                                              (ConsoleKey.NumPad0 <= key) && (key <= ConsoleKey.NumPad9)):
                        entrada += cki.KeyChar;
                        Console.Write(cki.KeyChar);
                        break;
                }
            }
        return entrada;
    }
    public static void Main()
    {
        Console.WriteLine("Insira o valor para X.");


        int x = int.Parse(lerNumeros());

        Console.WriteLine("\nO valor de X é '{0}'.", x);

        Console.ReadKey();

    }
}

Using if independent of the language version:

using System;

class Exemplo
{
    public static string lerNumeros()
    {
        ConsoleKeyInfo cki;
        string entrada = "";            
        while (true)
            if (Console.KeyAvailable)
            {
                cki = Console.ReadKey(true);
                if (cki.Key == ConsoleKey.Backspace){
                    if (entrada.Length == 0) continue;
                    entrada = entrada.Remove(entrada.Length - 1);
                    Console.Write("\b \b"); //Remove o último caractere digitado
                }    
                if (cki.Key == ConsoleKey.Enter)
                {
                    break;
                }
                if ((ConsoleKey.D0 <= cki.Key) && (cki.Key <= ConsoleKey.D9) ||
                    (ConsoleKey.NumPad0 <= cki.Key) && (cki.Key <= ConsoleKey.NumPad9))
                {
                    entrada += cki.KeyChar;
                    Console.Write(cki.KeyChar);
                }

            }
        return entrada;
    }

    public static void Main()
    {
        Console.WriteLine("Insira o valor para X.");


        int x = int.Parse(lerNumeros());

        Console.WriteLine("\nO valor de X é '{0}'.", x);

        Console.ReadKey();

    }
}

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