Now came the main part of studying the API for writing the code. In the book for programming in LUA, a first example was given, which was a simple example for combination of lua with C.

#include <stdio.h>
    #include <string.h>
    #include <lua.h>
    #include <lauxlib.h>
    #include <lualib.h>
    
    int main (void) {
      char buff[256];
      int error;
      lua_State *L = lua_open();   /* opens Lua */
      luaopen_base(L);             /* opens the basic library */
      luaopen_table(L);            /* opens the table library */
      luaopen_io(L);               /* opens the I/O library */
      luaopen_string(L);           /* opens the string lib. */
      luaopen_math(L);             /* opens the math lib. */
    
      while (fgets(buff, sizeof(buff), stdin) != NULL) {
        error = luaL_loadbuffer(L, buff, strlen(buff), "line") ||
                lua_pcall(L, 0, 0, 0);
        if (error) {
          fprintf(stderr, "%s", lua_tostring(L, -1));
          lua_pop(L, 1);  /* pop error message from the stack */
        }
      }
    
      lua_close(L);
      return 0; 

    } 

In this example, C's file handling is combined with lua stack. If there is no error, then the stack is pushed with the code and then popped toget printed output. 

This is just a brief working of this API.