Demo of Lua integrated with C

b.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>

int main (int argc, char *argv[]) {
  if (argc < 3) {
    fprintf(stderr, "Missing arguments. Use it like ./program <a> <b>\n");
    return 1;
  }

  lua_State *L = luaL_newstate();

  char *code = \
    "function add(a, b)\n" \
    "return a + b\n" \
    "end\n";

  /* interpret lua code stored in `code` */
  luaL_loadbuffer(L, code, strlen(code), "inline");
  lua_pcall(L, 0, 0, 0);

  /* call the function `add` defined by the previous snippet */
  lua_getglobal(L, "add");
  lua_pushnumber(L, atof(argv[1]));
  lua_pushnumber(L, atof(argv[2]));
  lua_pcall(L, 2, 1, 0);
  
  /* the result of the previous function is at the top of the stack (-1) */
  printf("Result: %lf\n", lua_tonumber(L, -1));

  lua_close(L);
  return 0;
}

shell.txt

$ gcc -Ilua-5.3.5/src/ lua-5.3.5/src/liblua.a -lm b.c -o add.out
$ ./add.out 12.4 1.3
Result: 13.700000