list<T> reverse issue RSS

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  merrittr

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  list<T> reverse issue

  Nov 09, 2017 04:44 AM|merrittr|LINK

  I have code like this 

  public List<int> train = new List<int>();
  train=train.Reverse();
  train1[0]=wagonId;
  train=train.Reverse();

  but the 2 lines where I am assignmg train to itself reversed I get 

  Compiler output: 
  TrainComposition.cs(29,16): error CS0029: Cannot implicitly convert type 'void' to 'System.Collections.Generic.List<int style="box-sizing:border-box;color:#525252;font-family:Menlo, Monaco, Consolas, 'Courier New', monospace;font-size:15px;">' 
  TrainComposition.cs(31,15): error CS0029: Cannot implicitly convert type 'void' to 'System.Collections.Generic.List<int style="box-sizing:border-box;">'</int></int>

  any idea what is wrong ... I am trying to add a list item to the left side is the point of the reversing

• • Reply
  PatriceSc

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  Re: list<T> reverse issue

  Nov 09, 2017 05:26 PM|PatriceSc|LINK

  Hi,

  See https://msdn.microsoft.com/en-us/library/b0axc2h2(v=vs.110).aspx

  Reverse doesn't produce a new reversed list. The current list is updated. So in short your code should just be :
  
  train.Reverse();

  As a side note is this is your full code ? You are just testing ? It seems you'll run into another error (trying to access a non existing element plus reversing the list seems to serve no purpose at all).

  Edit: ah missed what you needed. So you want to use (from https://msdn.microsoft.com/en-us/library/sey5k5z4(v=vs.110).aspx ) :

  train.InsertAt(wagonId,0); // will always insert at the beginning of the list without having to reverse/unreverse.

  IMO when you start to work with a class which is not familiar always have a look at the doc to get an idea about its capabilities.

• • Reply
  pankaj@dotne...

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  Re: list<T> reverse issue

  Nov 12, 2017 06:02 PM|pankaj@dotnetlooker|LINK

  Hi,

  As per your code :

  train=train.Reverse(); // It is giving the compilation error.

  Reverse() function has void as a return type & your are trying to assign void value to variable train which is accepting list of integers. See below its definition. 

  // public void Reverse();

  It reverses the order of the elements in the entire System.Collections.Generic.List<T> so no need to assign it back to list.

  See the demo code:

              List<int> train = new List<int>();
              train.Add(1);
              train.Add(2);
              
              train.Insert(0, 3); // or train[0] = 5; 
              // You can add wagonId either by giving array index to list or by using List<T> Insert() function where the first argument is index 
              // of list & second argument is the item needs to be insert.
              
              train.Reverse();
              foreach (var item in train)
              {
                  Console.WriteLine(item);
              }
              Console.ReadLine();

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