C# -> string.Reverse(); - do not work in # using System.Linq;

Question

This program is not working as expected and I'm not sure why. The error is CS0266 " Error CS0266 Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<char>' to 'string'. An explicit conversion exists (are you missing a cast?)

BUT, it should work properly under using System.Linq;

using System;
using System.Linq;
namespace centuryyearsminutes
{
    class Program
    {
        static void Main(string[] args)
        {
            string aa = "Hello World!";
            string bb = aa.Reverse();
            Console.WriteLine(bb);
        }
    }
}

Linq's Reverse treats a string as an array of characters, and returns a collection of characters, not a string. — canton7
– canton7, Commented Nov 9, 2019 at 19:04
The compiler says you a) The return value of String.Reverse() is not a string, but a IEnumerable<char> (a special use case of the array). b) It can not find any implicit conversions between IEnumerable<char> and string — Christopher
– Christopher, Commented Nov 9, 2019 at 19:07
Note though that reversing a string character by character will produce the wrong result in lots of cases. — canton7
– canton7, Commented Nov 9, 2019 at 19:16
Does this answer your question? Best way to reverse a string — canton7
– canton7, Commented Nov 9, 2019 at 19:20

Charles · Accepted Answer · 2019-11-09 19:12:31Z

10

aa.Reverse() returns just an Enumerable<char>

try:

string bb = new string(aa.Reverse().ToArray());

Although this is probably the best way to do it:
https://stackoverflow.com/a/15111719/11808788

edited Nov 9, 2019 at 19:12

answered Nov 9, 2019 at 19:05

Charles

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CEH · Accepted Answer · 2019-11-09 19:13:16Z

8

.Reverse() is expecting a collection of characters (docs), not a string. If you do:

string aa = "Hello World!";

var result = aa.ToCharArray().Reverse();

Console.WriteLine(new string(result.ToArray()));

The output is !dlroW olleH.

This should work as expected.

edited Nov 9, 2019 at 19:13

answered Nov 9, 2019 at 19:05

CEH

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4 Comments

CEH Over a year ago

If you'd like to point out something wrong with an answer, feel free to comment and let me know how I can improve -- downvoting without any explanation doesn't help me understand much here :(

canton7 Over a year ago

There's no need for ToCharArray (that creates a new unnecessary array), and there's no String ctor which takes an IEnumerable. The downvote is probably because your code won't compile (though it's not mine)

CEH Over a year ago

I missed a .ToArray() cast on the new string() call. The code compiles and produces a reversed string.

canton7 Over a year ago

It does now. It's always worth testing the code you post. The ToCharArray is still unnecessary though.

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