Replace values in string

Assuming you have your Regex correctly setup, you can utilize one of the overloads of Regex.Replace to include a MatchEvaluator delegate. The MatchEvaluator is a Func<Match,string> delegate (meaning any public string Method(Match match) method will work as input), with the return value being what you want to replace the original string with. The regex for the search is (@\S+) which means "Match the @ symbol, followed by any non-whitespace character (\S) at least once (+).

Regex.Replace(input, "(@\S+)", (match) => { /* Replace logic here. */ })

Running the above regex on the input @yahoo.com is going to be @simple for purposes of @matching., it matches on @yahoo.com, @simple and @matching. (notice that it includes punctiation on the @matching.).

Hope that helps!

If you're writing in C#, a regex is probably your best option. The code is quite simple

MatchCollection matches = Regex.Matches(/*input*/, /*pattern*/)
foreach (Match m in matches)
{
    /*Do work here*/
}

For learning regular expressions and the syntax associated, I used http://www.regular-expressions.info/tutorial.html to get started. A lot of good information in there, and easy to read.

For example:

string str = "@yahoo aaaa bbb";
string replacedStr = str.Replace("@yahoo", "replacement");

Look to documentation: string.Replace

Try using String.Replace() function:

String x="lalala i like being @Yahoo , my Email is [email protected]";

x=x.Replace("@Yahoo","@Gmail");

X will be now : "lalala i like being @Gmail, my Email is [email protected]";

To know where the next space after "@Yahoo", use location variable, with String.IndexOf() and String.LastIndexOf().

int location=x.IndexOf("@Yahoo");//gets the location of the first "@Yahoo" of the string.

int SpaceLoc=x.IndexOf("@Yahoo",location);// gets the location of the first white space after the first "@Yahoo" of the string.

Hope that helps.

Do you mean ampersand & or at-symbol @?

This should do what you need: &([\S\.]+)\b

or for the at-symbol: @([\S\.]+)\b

I think a RegEx.Replace is your best bet. You can simply do something like this:

string input = "[email protected] is my email address";
string output = Regex.Replace(input, @"@\S+", new MatchEvaluator(evaluateMatch));

And you just need to define the evaluateMatch method, such as:

private string evaluateMatch(Match m)
{
    switch(m.Value)
    {
        case "@yahoo.com": 
            return "@google.com";
            break;
        default:
            return "@other.com";
    }
}