IsInteger

Returns true if the given string can be parsed into an integer, false otherwise.

• Return the result of calling Double.TryParse() with NymberStyles.Integer for the given num string.
• Use Double.TryParse() to allow handling of values larger than Int64.

using System.Globalization;

public static partial class _30s 
{
  public static bool IsInteger(string num) 
  {
    Double _ = 0.0;
    return Double.TryParse(num, NumberStyles.Integer, NumberFormatInfo.CurrentInfo, out _);
  }
}

_30s.IsInteger("2"); // true
_30s.IsInteger("3.1"); // false