String Search & replacement

I have a string "JohnMarkMarkMark"

I want to replace the "Mark" with "Tom" with two cases

In first case i want to replace only first occurance of "Mark" Result will be: "JohnTomMarkMark" In the second case i want to replace all the occuran开发者_开发技巧ce of "Mark" Result will be: "JohnTomTomTom"

Please suggest Thnaks

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string data = "JohnMarkMarkMark";
string resultOne = new Regex("Mark").Replace(data,  "Tom", 1);
string resultAll = data.Replace("Mark", "Tom");

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For the first case, use IndexOf, Substring and Concat.

For the second case, use Replace.

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(1) is:

var inString = "TestMarkMarkMark";

var lookFor = "Mark";
var replaceWith = "Tom";
var length = lookFor.Length;
var first = inString.IndexOf(lookFor);
var newString = inString.Substring(0, first) + replaceWith + inString.Substring(first + length);

Which could be optimized, but I've expanded it out so it's easy to follow.

(2) is trivial - just do inString.Replace("Mark", "Tom");

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for case 1 try this

            string s = "JohnMarkMarkMark";
            Regex x = new Regex("Mark");
            MatchCollection m = x.Matches(s);
            if (m!=null && m.Count > 0)
            {
                s = s.Remove(m[0].Index, m[0].Length);
                s = s.Insert(m[0].Index,"Tom");
            }

for case 2 try s = s.Replace("Mark","Tom");