Data commit

Task/Descending-primes/C/descending-primes.c

@@ -0,0 +1,24 @@
+#include <stdio.h>
+
+int ispr(unsigned int n) {
+    if ((n & 1) == 0 || n < 2) return n == 2;
+    for (unsigned int j = 3; j * j <= n; j += 2)
+      if (n % j == 0) return 0; return 1; }
+
+int main() {
+  unsigned int c = 0, nc, pc = 9, i, a, b, l,
+    ps[128], nxt[128];
+  for (a = 0, b = 1; a < pc; a = b++) ps[a] = b;
+  while (1) {
+    nc = 0;
+    for (i = 0; i < pc; i++) {
+        if (ispr(a = ps[i]))
+          printf("%8d%s", a, ++c % 5 == 0 ? "\n" : " ");
+        for (b = a * 10, l = a % 10 + b++; b < l; b++)
+          nxt[nc++] = b;
+      }
+      if (nc > 1) for(i = 0, pc = nc; i < pc; i++) ps[i] = nxt[i];
+      else break;
+    }
+    printf("\n%d descending primes found", c);
+}