CODEWITHSUNDEEP
c#
user732853
user732853

Reputation: 521

How to replace last character of the string using c#?

string str = "Student_123_";

I need to replace the last character "_" with ",". I did it like this. 

str.Remove(str.Length -1, 1);
str = str + ",";

However, is it possible to achieve it more efficiently. may be one line of code.?? BTW, last character can be any character. So Replace wont work here.

Upvotes: 49

Views: 119769

Answers (11)

user8604852
user8604852

Reputation: 1

//You mean like this? :D
string str = "Student_123_";
str = $"{str.Remove(str.Length -1)},";

Upvotes: 0

Vlad
Vlad

Reputation: 13

// As string is array of chars you can use efficient "range" operator introduced in c# 8.0
string str = "Student_123_";
str = str[0..^1] + ",";

Upvotes: 1

bbosak
bbosak

Reputation: 5529

Use the StringBuilder class 

StringBuilder mbuilder = new StringBuilder("Student_123_");
mbuilder[mbuilder.Length-1] = ',';
Console.WriteLine(mbuilder.ToString());

Upvotes: 7

Ryan Williams
Ryan Williams

Reputation: 1620

Elegant but not very efficient. Replaces any character at the end of str with a comma.

str = Regex.Replace(str, ".$", ",");

Upvotes: 8

B H
B H

Reputation: 1878

C# .NET makes it almost too easy.

str = str.TrimEnd('_')

Upvotes: 35

user195488
user195488

Reputation:

str = str.Substring(0, str.Length-1) + ",";

Upvotes: 2

orlp
orlp

Reputation: 117681

No.

In C# strings are immutable and thus you can not change the string "in-place". You must first remove a part of the string and then create a new string. In fact, this is also means your original code is wrong, since str.Remove(str.Length -1, 1); doesn't change str at all, it returns a new string! This should do:

str = str.Remove(str.Length -1, 1) + ",";

Upvotes: 85

Jonathan Wood
Jonathan Wood

Reputation: 67193

That's a limitation of working with string. You can use StringBuilder if you need to do a lot of changes like this. But it's not worth it for the simple task you need.

str = str.Substring(0, str.Length - 1) + ",";

Upvotes: 7

David Yaw
David Yaw

Reputation: 27864

str.Remove doesn't modify str, it returns a new string. Your first line should read str = str.Remove...

One line? OK: str = str.Remove(str.Length - 1) + ",";

I think that's as efficient as you're going to get. Technically, you are creating two new strings here, not one (The result of the Remove, and the result of the Concatenation). However, everything I can think of to not create two strings, ends up creating more than 1 other object to do so. You could use a StringBuilder, but that's heavier weight than an extra string, or perhaps a char[], but it's still an extra object, no better than what I have listed above.

Upvotes: 1

coldandtired
coldandtired

Reputation: 1043

With one line of code you could write:

str = str.Remove(str.Length - 1, 1) + ",";

Upvotes: 2

debracey
debracey

Reputation: 6597

Well, what you have won't work because str.Remove(...) doesn't manipulate str, it returns a new string with the removal operation completed on it.

So - you need:

str = str.Remove(str.Length-1,1);
str = str + ",";

In terms of efficiency, there are several other choices you could make (substring, trim ...) but ultimately you're going to get the same time/space complexity.

EDIT:

Also, don't try to squash everything into one line, the programmers who come after you will appreciate the greater readability. (Although in this case a single line is just as easy to read.) One line != more efficient.

Upvotes: 1

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