After String.Reverse, a mistake occurs in ToString

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.

What do you want to achieve? What is the content of `_subStr`? What should be the output? — juergen d, Feb 26 '12 at 11:31
This line of code is too hard to debug because it's doing too many different things. Try splitting up each step into its own line, then you can use the debugger to inspect the state of your variables between each intermediate step, and see where the problem is. — MattDavey, Feb 26 '12 at 11:34

score 9 · Accepted Answer · edited May 23 '17 at 12:16

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.

The reverse string point may be moot, because the string in question is representing a whole number (which will be reversed correctly in this case). — MattDavey, Feb 27 '12 at 10:15

score 1 · Answer 2 · answered Feb 26 '12 at 11:57

As the Reverse method is an extension of IEnumerable<T>, you get an IEnumerable<T> as result, and as that doesn't override the ToString method, you will get the original implementation from the Object class, that simply returns the type name of the object. Turn the IEnumerable<T> into an array, then you can create a string from it.

You should first get the part of the string that is digits, then reverse it. That way it will work, regardless of what characters you have in the rest of the string. Although using the Reverse extension doesn't work properly to reverse any string (as Thomas Levesque pointed out), it will work for a string with only digits:

(
  Int32.Parse(
    new String(_subStr.SubString(0, _subStr.Length - 4).Reverse().ToArray())
  ) * 1.6
).ToString();

score 0 · Answer 3 · edited Dec 29 '21 at 17:30

the simplest approach would be:

string backwards = "sdrawkcab";
string reverse = "";
for(int i = backwards.Length-1; i >= 0; i--)
     reverse += backwards[i];

The result is: reverse == "backwards".

then you can do:

reverse = (Convert.ToInt32(reverse) * 1.6).toString();

Your Piping approach string.Substring().Split().Last()... will very quickly lead to a memory bottleneck, if you loop through lines of text.

Also important to notice: strings are Immutable, therefor each iteration of the for loop we create a new string instance in the memory because of the += operator, this will give us less optimal memory efficieny compared to other, more efficient algorithms, this is an O(n2) algorithm.

for a more efficient implementation you can check: https://stackoverflow.com/a/1009707/14473033

After String.Reverse, a mistake occurs in ToString

3 Answers3