C# Pass criteria of input validation as parameter

Question

I have simple function of input validation:

private static int GetInt()
{
    int tryInt;

    while (true)
    {
        if (int.TryParse(Console.ReadLine(), out tryInt)) 
            return tryInt;
        else 
            Console.Write("Try again:");
    }
}

I want to pass in criteria (let's say I want odd numbers, more than 20) How can I do it? Should I?

private static int GetInt(< criteria >)
{
    int tryInt;

    while (true)
    {
        if (int.TryParse(Console.ReadLine(), out tryInt) && < criteria >) 
           return tryInt;
        else 
           Console.Write("Try again:");
    }
}

Sergey Sosunov · Accepted Answer · 2024-12-26 07:17:56Z

2

Sounds like you can utilize Func delegates

Example:

using System;

public class Program
{
    public static void Main()
    {
        int number = GetInt();
        Console.WriteLine($"You entered: {number}");
        
        int number2 = GetInt(n => n > 0 && n < 100);
        Console.WriteLine($"You entered: {number2}");
        
        Func<int, bool> isPositiveCriteria = number => number > 0;
        int number3 = GetInt(isPositiveCriteria);
        Console.WriteLine($"You entered: {number3}");
    }

    private static int GetInt(Func<int, bool>? additionalValidation = null)
    {
        int tryInt;
        while (true)
        {
            Console.Write("Enter a number: ");
            if (int.TryParse(Console.ReadLine(), out tryInt) && (additionalValidation == null || additionalValidation(tryInt)))
            {
                return tryInt;
            }

            Console.WriteLine("Invalid input. Try again:");
        }
    }
}

Dotnet fiddle playground

answered Dec 26, 2024 at 7:17

Sergey Sosunov

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1 Comment

Simcha Bryzgalov Dec 26, 2024 at 14:35

Thanks, that exactly what I was looking for.

Karen Payne · Accepted Answer · 2024-12-26 11:38:42Z

1

An elegant solution is using Spectre.Console NuGet package, using Text prompt which as shown accepts an int with, in this case validates the value entered is an int and the value entered here is between 1 and 10. Also uses colors to are optional.

Code written using NET 9.

internal class Prompts
{
    public static int GetInt(string title = "Enter a number") =>
        AnsiConsole.Prompt(
            new TextPrompt<int>($"[yellow]{title}[/]?")
                .PromptStyle("cyan")
                .Validate(ValidateBetweenOneAndTen)
                .ValidationErrorMessage("[red]Must be an integer[/]"));

    private static ValidationResult ValidateBetweenOneAndTen(int value) =>
        value is >= 1 and <= 10 ? 
            ValidationResult.Success() : 
            ValidationResult.Error("Must be between 1 and 10");
}

Usage:

internal partial class Program
{
    static void Main(string[] args)
    {

        var number = Prompts.GetInt();
        Console.Clear();
        AnsiConsole.MarkupLine($"[bold]You entered[/]: [yellow]{number}[/]");
        Console.ReadLine();
    }
}

answered Dec 26, 2024 at 11:38

Karen Payne

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1 Comment

Simcha Bryzgalov Jan 9 at 5:19

Thank you very much for your answer! I am going to use it.

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