Data commit

Task/Descending-primes/C-sharp/descending-primes.cs

@@ -0,0 +1,28 @@
+using System;
+
+class Program {
+
+  static bool ispr(uint n) {
+    if ((n & 1) == 0 || n < 2) return n == 2;
+    for (uint j = 3; j * j <= n; j += 2)
+      if (n % j == 0) return false; return true; }
+
+  static void Main(string[] args) {
+    uint c = 0; int nc;
+    var ps = new uint[]{ 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+    var nxt = new uint[128];
+    while (true) {
+      nc = 0;
+      foreach (var a in ps) {
+        if (ispr(a))
+          Console.Write("{0,8}{1}", a, ++c % 5 == 0 ? "\n" : " ");
+        for (uint b = a * 10, l = a % 10 + b++; b < l; b++)
+          nxt[nc++] = b;
+      }
+      if (nc > 1) {
+        Array.Resize (ref ps, nc); Array.Copy(nxt, ps, nc); }
+      else break;
+    }
+    Console.WriteLine("\n{0} descending primes found", c);
+  }
+}