using System;
using System.Text;
class Program
{
static string string_char_toupper(string s, int idx) {
int len = s.Length;
if (idx > len || idx < 0) return s;
StringBuilder sb = new StringBuilder(s);
sb[idx] = Char.ToUpper(sb[idx]);
return sb.ToString();
}
static void Main() {
string s = "c# programming";
s = string_char_toupper(s, 3);
Console.Write(s);
}
}
/*
run:
c# Programming
*/