Number of occurrences of a character in a string [duplicate]

You could do this:

int count = test.Split('&').Length - 1;

Or with LINQ:

test.Count(x => x == '&');

Because LINQ can do everything...:

string test = "key1=value1&key2=value2&key3=value3";
var count = test.Where(x => x == '&').Count();

Or if you like, you can use the Count overload that takes a predicate :

var count = test.Count(x => x == '&');

The most straight forward, and most efficient, would be to simply loop through the characters in the string:

int cnt = 0;
foreach (char c in test) {
  if (c == '&') cnt++;
}

You can use Linq extensions to make a simpler, and almost as efficient version. There is a bit more overhead, but it's still surprisingly close to the loop in performance:

int cnt = test.Count(c => c == '&');

Then there is the old Replace trick, however that is better suited for languages where looping is awkward (SQL) or slow (VBScript):

int cnt = test.Length - test.Replace("&", "").Length;

Why use regex for that. String implements IEnumerable<char>, so you can just use LINQ.

test.Count(c => c == '&')