add timer to c program

exercises/hpc_example.cpp

@@ -6,6 +6,7 @@
 #include <string.h>
 #include <unistd.h>
 #include <limits.h>
+#include <time.h>
 #include <iostream>       // std::cout, std::endl
 #include <thread>         // std::this_thread::sleep_for
 #include <chrono>         // std::chrono::seconds
@@ -18,15 +19,15 @@ int main(int argc,char* argv[])
     std::vector <std::string> sources;
     int *a;
     size_t mem = 0;
-    int time = 10;
+    int waittime = 10;
     char hostname[HOST_NAME_MAX];
-
+    time_t t1, t2;
 
     for (int i = 1; i < argc; ++i) {
         if (std::string(argv[i]) == "-t") {
             if (i + 1 < argc) { // Make sure we aren't at the end of argv!
                 std::stringstream ss1(argv[++i]);
-                if (!(ss1 >> time))
+                if (!(ss1 >> waittime))
                   std::cerr << "Invalid number " << argv[i] << '\n';
             } else { // Uh-oh, there was no argument to the destination option.
                   std::cerr << "-t option requires one argument." << std::endl;
@@ -46,19 +47,23 @@ int main(int argc,char* argv[])
         }
     }
 
+    time(&t1);
+
     int result = gethostname(hostname, HOST_NAME_MAX);
     std::string hostname2 = hostname;
 
     std::cout << "Current host is: " + hostname2 << std::endl;
-    std::cout << "Wait time is: " << time << " seconds" << std::endl;
+    std::cout << "Wait time is: " << waittime << " seconds" << std::endl;
     std::cout << "Memory usage is: " << mem << "MB" << std::endl;
 
     long int l = mem * 1024 * 1024;
 
     a = (int*)calloc(mem, 1024 * 1024);
     memset(a, 0, mem * 1024 * 1024);
-    std::this_thread::sleep_for (std::chrono::seconds(time));
+    std::this_thread::sleep_for (std::chrono::seconds(waittime));
     free(a);
 
+    time(&t2);
+    std::cout << "Actually running time: " << difftime(t2, t1) << " seconds" << std::endl;
     return 0;
 }