Method that returns an integer chosen by user
You should start using comparison operators,

for a range from 1 to 4, use this:

if (oneFour &gt;= 1 &amp;&amp; oneFour &lt;= 4)


This reads naturally as "if variable is more than or equal to 1 and variable is less then or equal to 4", which is the same thing as "if variable is in range 1 to 4".

Other improvements:


Instead of setting the isError value, you can return oneFour; directly.
Using the above advice, you can change your loop to while (true), eliminating your isError totally.
Using the above advice, you can make the scope for the oneFour variable smaller, which is a good thing (when possible).
Braces. Always use braces.


Resulting code will look something like this:

static int oneToFour()
{
    while (true)
    {
        try
        {

            int oneFour = Convert.ToInt32(Console.ReadLine());
            if (oneFour == 1 || oneFour == 2 || oneFour == 3 || oneFour == 4)
            {
                return oneFour;
            }
            else
            {
                Console.WriteLine(_warning);
            }
        }
        catch { Console.WriteLine(_warning); }
    }
}