Game development Path finding

#define WIN32_LEAN_AND_MEAN		
#include <windows.h>
#include <stdlib.h>
#include <malloc.h>
#include <memory.h>
#include <tchar.h>
#include <stdio.h>
 
//include the engine data types, variables, and functions
#include "adll.h"
#include "init_engine.h"
#include "grid.h"
 
ENTITY* gStartEnt = NULL;    //pointer to start entity
ENTITY* gGoalEnt = NULL;     //pointer to goal entity
int gStartNode = -1;         //start node, initialized to -1
int gGoalNode = -1;          //goal node, initialized to -1
 
 
//draw path from goal position to goal node, then along all connections back to start node, then to start position
void draw_path()
{
  COLOR cColour; //colour vector
  VECTOR vTemp;  //temp vector
  
  //set the colour to light grey
  cColour.blue = _VAR(0);
  cColour.green = _VAR(255);
  cColour.red = _VAR(255);                                                                                                  
 
  //set temp vector to goal position
  vTemp.x = gGoalEnt->x;
  vTemp.y = gGoalEnt->y;
  vTemp.z = _VAR(30); 
  //place the draw position there, (pass colour as NULL because don't want to start drawing yet)
  draw_line3d(&vTemp, NULL, _VAR(100));
  //set it to the correct colour
  draw_line3d(&vTemp, &cColour, _VAR(100));
  
  //set temp vector to goal position
  vTemp.x = gStartEnt->x;
  vTemp.y = gStartEnt->y;
  vTemp.z = _VAR(30); 
  draw_line3d(&vTemp, &cColour, _VAR(100));
}
 
//this function handles left mouse clicks
void handle_leftclick()
{
  VECTOR position;     //temp position variable
  int i, closest_node;     //for loop counter and variable for closest node found so far
  float closest_distance, temp_distance;      //variables for closest distance found so far and temp distance
  
  //if there is no start node
  if(gStartNode == -1)
  {
    if(get_position(&position, gStartNode))    //if mouse clicked on valid position
    {
      gStartEnt = ent_create("blue_target.mdl", &position, NULL); //create entity at start position
    }
  }
  //if there is no goal node
  else if(gGoalNode == -1)
  {
    if(get_position(&position, gGoalNode))      //if mouse clicked on valid position
    {
      gGoalEnt = ent_create("target.mdl", &position, NULL);        //create entity at goal position
 
      draw_path();
/////////////////////////////////////////////////////////////////////////////////////////////////////    
//CALL YOUR PATH FINDING FUNCTION HERE
 
///////////////////////////////////////////////////////////////////////////////////////////////////// 
    }
  }
  else       //reset
  {
    if(gStartEnt != NULL)     //check whether there is a start entity (just in case)
    {
      ent_remove(gStartEnt);  //remove entity
      gStartEnt = NULL;       //reset pointer to NULL
    }
    if(gGoalEnt != NULL)      //check whether there is a goal entity (just in case)
    {
      ent_remove(gGoalEnt);   //remove entity
      gGoalEnt = NULL;        //reset pointer to NULL
    }
    gStartNode = -1;          //reset start node
    gGoalNode = -1;           //reset goal node
    
    reset_node_records();     //reset node records
  }
}
 
//main function
int APIENTRY WinMain(HINSTANCE hInstance,	
                     HINSTANCE hPrevInstance,
                     LPTSTR    lpCmdLine,	
                     int       nCmdShow)	
{
  engine_init();     //calls function that initializes the engine
 
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
  //initialise everything you need before entering main rendering loop
 
  init_grid();            //setup the grid
  reset_node_records();   //initialize the node records
 
  //assign function for left mouse click
  v(on_mouse_left) = (EVENT)handle_leftclick;
 
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////
  //main rendering loop, this will loop once every frame until you quit
  while(engine_frame()) 
  {
    //update debug text display
    update_debug_text();
  }
  
  //DO NOT CHANGE
  engine_close();     //engine frees all created entities, bitmaps and sounds automatically when closing
  return 0;
}