"Input string was not in a correct format" when trying to print a List

Question

So I've been trying to do a program, which looked really simple at first, but I guess I must have underestimated it. The program is to receive 2 List with Console.ReadLine() and then merge them in a 3rd list, then List.Sort and print it.

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

namespace Array.Merge
{
    class Program
    {
        static void Main(string[] args)
        {
            string input1 = Console.ReadLine();
            string input2 = Console.ReadLine();
            List numbers1 = input1.Split(" ").Select(int.Parse).ToList();
            List numbers2 = input2.Split(" ").Select(int.Parse).ToList();
            List numbers = new List();
            for (int a = 0; a < numbers1.Count; a++)
            {
                numbers.Add(numbers1[a]);
            }
            for (int b = 0; b < numbers2.Count; b++)
            {
                numbers.Add(numbers2[b]);
            }
            numbers.Sort();
            foreach(int number in numbers)
            {
                Console.Write(number + " ");
            }
            
        }
    }
}

when I submit my 2 lines of input, I get the error "Input string was not in a correct format" in the console. This is the input I am using:

1 2 3 7 9 
2 4 5 7 8

This is what I should be receiving:

1 2 2 3 4 5 7 7 8 9

Tim Schmelter · Answer

You should always use TryParse methods if you handle user input
Split can contain empty results, if you have multiple consecutive spaces and don't use StringSplitOptions.RemoveEmptyEntries

So this should work and is double safe:

List numbers1 = input1.Split(' ', StringSplitOptions.RemoveEmptyEntries)
        .Select(s => (IsValid: int.TryParse(s, out int Value), Value))
        .Where(x => x.IsValid)
        .Select(x => x.Value)
        .ToList();
List numbers2 = input2.Split(' ', StringSplitOptions.RemoveEmptyEntries)
       .Select(s => (IsValid: int.TryParse(s, out int Value), Value))
       .Where(x => x.IsValid)
       .Select(x => x.Value)
       .ToList();

List numbers = numbers1.Concat(numbers2).OrderBy(i => i).ToList();

You can also create a (local) method to not repeat yourself:

List GetValidInts(string s) => s?.Split(' ', StringSplitOptions.RemoveEmptyEntries)
    .Select(s => (IsValid: int.TryParse(s, out int Value), Value))
    .Where(x => x.IsValid)
    .Select(x => x.Value)
    .ToList() ?? new List();

List numbers1 = GetValidInts(input1);
List numbers2 = GetValidInts(input1);

"Input string was not in a correct format" when trying to print a List

1 Answers