Replacing specific parts of a string in an array

Question

I'm pretty familiar with finding and replacing things in an array, but I'm having trouble finding out how to replace specific parts of a string. For instance, say the first item in my array is a string of sixteen random numbers like 1786549809654768. How would I go about replacing the first twelve characters with x's for example?

Answer 1

Because string can be translated to and from an array of char you could easily transform your problem into replace things in an array problem:

char[] characters = input.ToCharArray();

// do your replace logic here

string result = new string(characters);

Or you could use Substring. Assuming n is number of characters you want to replace from the beginning or the string:

string result = new string('x', n) + input.Substring(n);

Answer 2

You can use Linq:

String test = "1234123412341234";
string output = new String(test.Select((c, index) => index < 12 ? 'x' : c).ToArray());
Console.WriteLine(output);
//xxxxxxxxxxxx1234