Twin primes: Difference between revisions

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@@ Line 104: / Line 104: @@
 <lang cpp>#include <cstdint>
 #include <iostream>
+#include <string>
 #include <primesieve.hpp>
+void print_twin_prime_count(uint64_t limit) {
-int main() {
+    std::cout << "Number of twin prime pairs less than " << limit
+        << " is " << primesieve::count_twins(0, limit - 1) << '\n';
+}
+int main(int argc, char** argv) {
     std::cout.imbue(std::locale(""));
-    uint64_t limit = 10;
+    if (argc > 1) {
+        // print number of twin prime pairs less than limits specified
-    for (int power = 1; power < 12; ++power, limit *= 10) {
+        // on the command line
-        std::cout << "Number of twin prime pairs less than " << limit
-            << " is " << primesieve::count_twins(0, limit) << '\n';
+        for (int i = 1; i < argc; ++i) {
+            try {
+                print_twin_prime_count(std::stoull(argv[i]));
+            } catch (const std::exception& ex) {
+                std::cerr << "Cannot parse limit from '" << argv[i] << "'\n";
+            }
+        }
+    } else {
+        // if no limit was specified then show the number of twin prime
+        // pairs less than powers of 10 up to 100 billion
+        uint64_t limit = 10;
+        for (int power = 1; power < 12; ++power, limit *= 10)
+            print_twin_prime_count(limit);
     }
     return 0;