Find repeated characters in a string in C#

If you have a given string and you want to count the number of characters which are repeated in the string then you can use the following program.

public static void Main(string[] args)
{
int numberOfRepeatedChars=0;
char[] chars=new char[25];
string str="AAABCDEE";
char tocheck=(char)'a';
foreach(var i in str)
{
int charNo=0;
var asc=(char)i;
charNo++;
if(!chars.Contains((asc)))
{

chars[charNo]=asc;

}
else
{

numberOfRepeatedChars++;
}

}

Console.WriteLine(numberOfRepeatedChars);
}

the above program will print 2 as there are two characters which are repeated in the string which are A and E.

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