automatically define variable "gui_run" to contain the run number

tools/lammps-gui/codeeditor.cpp

@@ -417,6 +417,11 @@ void CodeEditor::setGroupList()
 void CodeEditor::setVarNameList()
 {
     QStringList vars;
+
+    // variable "gui_run" is always defined by LAMMPS GUI
+    vars << QString("${gui_run}");
+    vars << QString("v_gui_run");
+
     LammpsWrapper *lammps = &qobject_cast<LammpsGui *>(parent())->lammps;
     int nvar              = lammps->id_count("variable");
     char buffer[200];

tools/lammps-gui/lammpsgui.cpp

@@ -1002,6 +1002,10 @@ void LammpsGui::do_run(bool use_buffer)
     runner     = new LammpsRunner(this);
     is_running = true;
     ++run_counter;
+
+    // define "gui_run" variable set to run_counter value
+    lammps.command("variable gui_run delete");
+    lammps.command(std::string("variable gui_run index " + std::to_string(run_counter)).c_str());
     if (use_buffer) {
         // always add final newline since the text edit widget does not do it
         char *input = mystrdup(ui->textEdit->toPlainText() + "\n");