diff --git a/src/magtet.cpp b/src/magtet.cpp
index d75cab2..e9afe2f 100644
--- a/src/magtet.cpp
+++ b/src/magtet.cpp
@@ -498,3 +498,35 @@ void magtet::routine(const char *para_file)
 	RUN_ECHO(write_text(gopt_.get_value(OBSFILE)), "Writing outputs");
 	return;
 }
+
+// Here starts the main function
+int main(int argc, char const *argv[])
+{
+	if (argc == 1)
+	{
+		std::clog << "Magnetic gradient tensors of homologous tetrahedrons.\n";
+		std::clog << "Usage: ./magtet <para-file>\n";
+		std::clog << "Option format:\n";
+		std::clog << "<option> = <value>\n";
+		std::clog << "Available options:\n";
+		std::clog << "tet-file: 3D model file. this option needs both .node and .ele files generated by Tetgen. No file extension is needed\n";
+		std::clog << "mag-file: magnetization vectors. Line format: <magz-x> <magz-y> <magz-z>\n";
+		std::clog << "site-file: observation points. format1: <filename> format2: <xmin>/<xmax>/<ymin>/<ymax>/<z>/<xnum>/<ynum>\n";
+		std::clog << "site-file: line format: <x> <y> <z>\n";
+		std::clog << "obs-file: output observation files. No file extension is needed\n";
+		std::clog << "cal-type: available calculating types: potential, gradient and tensor\n";
+		return -1;
+	}
+
+	try
+	{
+		// declare a new object
+		magtet mt;
+		mt.routine(argv[1]);
+		return 0;
+	}
+	catch(std::exception &e)
+	{
+		GCTL_ShowWhatError(e.what(), GCTL_ERROR_ERROR, 0, 0, 0);
+	}
+}
diff --git a/src/main.cpp b/src/main.cpp
deleted file mode 100644
index ddb743e..0000000
--- a/src/main.cpp
+++ /dev/null
@@ -1,32 +0,0 @@
-#include "magtet.h"
-
-int main(int argc, char const *argv[])
-{
-	if (argc == 1)
-	{
-		std::clog << "Magnetic gradient tensors of homologous tetrahedrons.\n";
-		std::clog << "Usage: ./magtet <para-file>\n";
-		std::clog << "Option format:\n";
-		std::clog << "<option> = <value>\n";
-		std::clog << "Available options:\n";
-		std::clog << "tet-file: 3D model file. this option needs both .node and .ele files generated by Tetgen. No file extension is needed\n";
-		std::clog << "mag-file: magnetization vectors. Line format: <magz-x> <magz-y> <magz-z>\n";
-		std::clog << "site-file: observation points. format1: <filename> format2: <xmin>/<xmax>/<ymin>/<ymax>/<z>/<xnum>/<ynum>\n";
-		std::clog << "site-file: line format: <x> <y> <z>\n";
-		std::clog << "obs-file: output observation files. No file extension is needed\n";
-		std::clog << "cal-type: available calculating types: potential, gradient and tensor\n";
-		return -1;
-	}
-
-	try
-	{
-		// declare a new object
-		magtet mt;
-		mt.routine(argv[1]);
-		return 0;
-	}
-	catch(std::exception &e)
-	{
-		GCTL_ShowWhatError(e.what(), GCTL_ERROR_ERROR, 0, 0, 0);
-	}
-}
\ No newline at end of file