Move files into src folder.

CMakeLists.txt

@@ -2,11 +2,18 @@ cmake_minimum_required(VERSION 3.5.0)
 project(Test_Project VERSION 0.1.0 LANGUAGES C)
 
 # Add more c files in here
+# add_executable(Test_Project
+# main.c
+# hello.c
+# math_functions.c
+# struct_test.c
+# )
+
 add_executable(Test_Project
-main.c
-hello.c
-math_functions.c
-struct_test.c
+src/main.c
+src/hello.c
+src/math_functions.c
+src/struct_test.c
 )
 
 # https://discourse.cmake.org/t/how-to-properly-include-header-files/4762