c# change the string in a foreach string loop

Question

I'm trying to cycle through strings in a list with a foreach loop, but I don't know how to change the item that's being referenced - How can I change s in the list... e.g. below I want to add "-" to the end of every string, s in myStringList

foreach(string s in myStringList)
{
 s = s + "-"; 
}

I can't do things to s because it's a "foreach iteration variable" - so can I not change it as I cycle through?

Do I have to use an int to count through?

I'm sure there's a simpler way...

• mjwills: Have you considered using a for loop instead? myStringList[i] += "-";
• lolbas: Alternative way would be using LINQ expressions
• jamheadart: I have but I honestly thought there'd be a really simple "ref" keyword to chuck in and alter the s directly as I cycle through, with s.replace and s=s + x things like that.
• John Bustos: You can't change values while iterating through them in a foreach - You'd have to either use linq to change them or copy the (updated) values to a new collection
• xdtTransform: Possible duplicate of c# string.replace in foreach loop

Answer 1

You can do this with Linq quite easily:

var newStringList = myStringList
 .Select(s => s + "-")
 .ToList();

If you really want to modify the existing list, you can use a classic for loop, for example:

for (var i = 0; i < myStringList.Count; i++)
{
 myStringList[i] = myStringList[i] + "-";
}

• jamheadart: I take it this'd work with string functions too like .Select(s => s.Replace("-",""))
• DavidG: Yes, you're creating new strings and assigning the result to a completely new list. Remember that string is immutable in C# so you can never change it, only create new ones.
• jamheadart: Funny when you say a keyword and something clicks. Immutable! I'm with you.
• mjwills: A potential issue with the LINQ solution, since a completely new list has been created, is that any references to the old list won't see the change. This may not be an issue if this is the only reference to the list.
• vc 74: @mjwills If you really (unlikely) want to cover this case, you can var copy = list.Select(s => s + "-") .ToList(); list.Clear(); list.AddRange(copy)

Answer 2

Try this

List<string> listString = new List<string>() { "1","2","3"};
listString=listString.Select(x => x + "-").ToList();

• DavidG: I posted basically the same solution 10 minutes ago, how is yours any different?