Data commit

Task/Emirp-primes/C/emirp-primes.c

@@ -0,0 +1,52 @@
+#include <stdio.h>
+
+typedef unsigned uint;
+int is_prime(uint n)
+{
+        if (!(n%2) || !(n%3)) return 0;
+        uint p = 1;
+        while(p*p < n)
+                if (n%(p += 4) == 0 || n%(p += 2) == 0)
+                        return 0;
+        return 1;
+}
+
+uint reverse(uint n)
+{
+        uint r;
+        for (r = 0; n; n /= 10)
+                r = r*10 + (n%10);
+        return r;
+}
+
+int is_emirp(uint n)
+{
+        uint r = reverse(n);
+        return r != n && is_prime(n) && is_prime(r);
+}
+
+int main(int argc, char **argv)
+{
+        uint x, c = 0;
+        switch(argc) { // advanced args parsing
+        case 1: for (x = 11; c < 20; x += 2)
+                        if (is_emirp(x))
+                                printf(" %u", x), ++c;
+                break;
+
+        case 2: for (x = 7701; x < 8000; x += 2)
+                        if (is_emirp(x))
+                                printf(" %u", x);
+                break;
+
+        default:
+                for (x = 11; ; x += 2)
+                        if (is_emirp(x) && ++c == 10000) {
+                                printf("%u", x);
+                                break;
+                        }
+        }
+
+        putchar('\n');
+        return 0;
+}