Save "main.cpp" as "main.c"
Add "main.c" to project
remove "main.cpp" from project.
Fix the compiler errors in "main.c"; the simplest fix is adding "#include <stdbool.h>"
#ifdef __cplusplus
#include <cstdlib>
#else
#include <stdlib.h>
#include <stdbool.h>
#endif
Save the project as a template. (Note: I have never done this step myself.)
Use the template for future C SDL Projects.
Tim S.