C # Is any conversion missing?

The correction above is correct, also keep in mind that you should not add one to const

 num1 = cont + 1;

Since it will always give you as a result that "they are not symmetrical"

Your cycle for should be in one of the following ways:

for (int cont = 0; cont < var1.Length; cont++)

OR

for (int cont = 0; cont <= var1.Length - 1; cont++)

For example, if you have an array with 10 items, your major index will be 9, since .NET handles all arrays with indexes starting at 0, so if you use var1.Length (que para el ejemplo que te pongo seria igual a 10) when the cycle for reaches the Last you will try to access index 10, which does not exist within the arrangement and therefore will present the error that is happening to you.

How about something like this

  string var1 = Console.ReadLine();
        string[] separadores = { " " };

        string[] subCadenas = var1.Split(separadores, StringSplitOptions.RemoveEmptyEntries);
        if (subCadenas[0].Length == subCadenas[1].Length)
        {
            Console.WriteLine("son simetricos");
        }
        else {
            Console.WriteLine("no son simetricos");
        }
        Console.WriteLine(subCadenas[0].Length);

The Exception IndexOutOfRangeException occurs when you try to sign in to an element of the arrangement using an index outside the limit (major) or minor

To solve this error it would be enough to modify the condition of your for since the indexes start from 0 (first element) and end in (n -1) (last item)

for (int cont = 0; cont < var1.Length; cont++)

Update

With respect to validate if they are symmetrical or not. I could try this.

if (var1[cont] == ' ')
{
   if (((var1.Length - 1) - cont) == cont) Console.WriteLine("son simetricos");
   else Console.WriteLine("no son simetricos");
   break;
}

For what I understand what you want to do after all is that a user enter two different words, and that the system tells you if they have the same number of letters each, no matter what they are.

I made a small code that does that. You can try it on link

//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

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

namespace Rextester
{
public class Program
{
    public static void Main(string[] args)
    {
        //Your code goes here
        var temporal = Console.ReadLine();
    //Con la instrucción que esta abajo, separo las palabras por el espacio vacío que hay entre ellas y genero un arreglo.
        var palabras = temporal.Split(' ');

        //valido que sean al menos dos palabras 
        if(palabras.Length > 1){
            if(palabras[0].Length == palabras[1].Length){
                Console.WriteLine("Son iguales");
            }else{
                Console.WriteLine("No son iguales");
            }
        }else{
            Console.WriteLine("Debe ingresar por lo menos dos palabras.");
        }
    }
}
}

Making adjustments to the code you can put the number of words you want and compare each one using a little imagination:

//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

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

namespace Rextester
{
public class Program
{
    public static void Main(string[] args)
    {
        //Your code goes here
        var temporal = Console.ReadLine();
        var palabras = temporal.Split(' ');

        //valido que sean al menos dos palabras 
        if(palabras.Length > 1){

            var numeroLetras = 0;
            bool iguales = true;
            foreach(string temp in palabras){
                if(numeroLetras != 0 && numeroLetras != temp.Length){
                    iguales = false;
                }
                numeroLetras = temp.Length;
            }

            if(iguales){
                Console.WriteLine("Todas las palabras tienen el mismo largo");
            }else{
                Console.WriteLine("Las palabras tienen distinto numero de letras.");
            }
        }else{
            Console.WriteLine("Debe ingresar por lo menos dos palabras.");
        }
    }
}
}

This is how it looks on the page that I sent you, to get the input, you must click on the plus sign that appears as a minus sign in the photo, where the cursor is.

I hope I helped you friend. Greetings!