Resolve "make interaction counter conform with output format"

Closes #640 (closed)

applications/c8_air_shower.cpp

@@ -602,8 +602,12 @@ int main(int argc, char** argv) {
 
     // directory for outputs
     string const outdir(app["--filename"]->as<std::string>());
-    string const labHist_file = outdir + "/inthist_lab_" + to_string(i_shower) + ".npz";
-    string const cMSHist_file = outdir + "/inthist_cms_" + to_string(i_shower) + ".npz";
+    // construct the directory for this library
+    boost::filesystem::create_directories(outdir + "/interaction_hist");
+    string const labHist_file =
+        outdir + "/interaction_hist" + "/inthist_lab_" + to_string(i_shower) + ".npz";
+    string const cMSHist_file =
+        outdir + "/interaction_hist" + "/inthist_cms_" + to_string(i_shower) + ".npz";
 
     // setup particle stack, and add primary particle
     stack.clear();