IntegerParser.cs

public static class IntegerParser
{
    private const int MinDigit = '0';
    private const int MaxDigit = '9';

    public static bool TryParse(object number, out int result)
    {
        if (number is int)
        {
            result = (int)number;

            return true;
        }

        if (number is string)
        {
            return ParseString((string)number, out result);
        }

        throw new NotSupportedException($"{nameof(IntegerParser)} only accepts strings ans integers, type '{number.GetType()}' is not supported");
    }

    private static bool ParseString(string number, out int result)
    {
        result = 0;
        for (var i = 0; i < number.Length; i++)
        {
            var charCode = (int)number[i];
            if (charCode < MinDigit || charCode > MaxDigit)
            {
                return false;
            }

            result = result * 10 + (charCode - MinDigit);
        }

        return true;
    }
}