Question

When the application runs, the IDE tells me Input string is not in the correct format.

(Convert.ToInt32(_subStr.Reverse().ToString().Substring(4, _subStr.Length - 4))*1.6).ToString() 

I don’t know how the Reverse() can be exactly used here.

Answer 1

There is no Reverse method in the String class, so the method you’re using is actually the Enumerable.Reverse extension method. This compiles because String implements IEnumerable<char>, but the result is not a string, it’s another implementation of IEnumerable<char>. When you call ToString() on that, you get this: System.Linq.Enumerable+<ReverseIterator>d__a01[System.Char]`.

If you want to convert this IEnumerable<char> to a string, you can dot it like this:

string reversed = new string(_subStr.Reverse().ToArray());
(Convert.ToInt32(reversed.Substring(4, _subStr.Length - 4))*1.6).ToString()

Note, however, that it is not a correct way of reversing a string, it will fail in some cases due to Unicode surrogate pairs and combining characters. See here and there for explanations.