1 files changed, 40 insertions, 0 deletions
diff --git a/contrib/bc/Examples/twins.b b/contrib/bc/Examples/twins.b
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+
+/* An example that finds all primes between 2 and limit. */
+
+define primes (limit) {
+    auto num, p, root, i
+
+    prime[1] = 2;
+    prime[2] = 3;
+    num = 2;
+    scale = 0;
+
+    for ( p=5; p <= limit; p += 2)  {
+	root = sqrt(p);
+	isprime = 1;
+	for ( i = 1;  i < num && prime[i] <= root; i++ ) {
+	    if ( p % prime[i] == 0 ) {
+		isprime = 0;
+		break;
+            }
+	}
+	if (isprime) {
+	    num += 1;
+	    prime [num] = p;
+	}
+     }
+}
+
+
+print "\ntyping 'twins (10)' will print all twin primes less than 10.\n"
+
+define twins (limit) {
+   auto i;
+
+   i = primes(limit+2);
+
+   for (i=1; prime[i] > 0; i++) {
+      if ((prime[i]+2) == prime[i+1]) \
+	print "twins are ", prime[i], " and ", prime[i+1], "\n"
+   }
+}