how to replace only first character of a string in C#

Question

I want to replace the character 'A' of the first character of a string if the first character is 0.

Data 01234500

Expected output A1234500

code

results getting - A12345AA


string formattedId = "01234500";
if(formattedId.Substring(0,1)=="0")
formattedId = formattedId.Replace("0","A");
Console.WriteLine(formattedId);

score 2 · Answer 1 · answered Feb 24 '23 at 17:18

2

The Replace() method always changes ALL instances of the targeted string. Instead, you can do this:

string formattedId = "01234500";

if(formattedId[0] == '0')
{
    formattedId = "A" + formattedId.Substring(1);
}
Console.WriteLine(formattedId);

answered Feb 24 '23 at 17:18

Joel Coehoorn

399,467
113
570
794

formattedId[0] not working , its working for formattedId.Substring(0,1) – dotnetdev1 Feb 24 '23 at 17:24
1

@dotnetdev1 That's because `formattedId[0]` is only a character, not a string, which is why my answer has single quotes on the right-hand side of the equality expression. This will be significantly more efficient than the `StartsWith()` option. – Joel Coehoorn Feb 24 '23 at 17:45

Ivan Vydrin · Accepted Answer · 2023-02-25T06:47:13.187

0

You can use StartsWith() to check the first char and Substring(1) to get the part after first char:

string formattedId = "01234500";
if (formattedId?.StartsWith("0") is true)
{
    formattedId = "A" + formattedId.Substring(1);
}
Console.WriteLine(formattedId); // Output: A1234500

edited Feb 25 '23 at 06:47

answered Feb 24 '23 at 17:20

Ivan Vydrin

273
7

how to replace only first character of a string in C#

2 Answers2