Collection

You can replace all occurrences of a particular character or sub-string using the String class's Replace method:

http://msdn.microsoft.com/en-us/library/system.string.replace(v=vs.110).aspx

For example:

   string s = "abcabc";
   s = s.Replace("abc", "def"); // string is now "defdef" 

More complex replacements can be made using regular expressions and the Regex.Replace method.

Notice that, since strings are immutable in .NET, these methods actually create new strings rather than altering the old ones.

You can effect replacements in indexed mutable collections such as arrays or lists by simply assigning new values to the element at a particular index.

For example:

int[] ia = {1, 2, 3};

ia[1] = 4; // array elements are now 1, 4, 3