program writes forces to file

main.cpp

 #include <iostream>
-#include "lib/nBodySim.h"
+#include <string>
+#include "lib/nBodySim.hpp"
 
 int main(int argc, char** argv) {
     std::string datafile;
 
     switch (argc) {
         case 1:
-            datafile = "lib/data.ascii";
+            datafile = "../data/data.ascii";
             break;
         case 2:
             datafile = argv[1];
@@ -17,9 +18,11 @@ int main(int argc, char** argv) {
     }
 
     nBodySim sim(datafile);
+    std::cout << "N = " << sim.getN() << std::endl;
 
     try {
-        sim.run();
+        sim.calculateForces();
+        sim.write2file(sim.getForces(), "../data/output.txt", sim.getN(), 3);
     } catch (std::exception& e) {
         std::cerr << e.what() << std::endl;
         return 1;