diff --git a/main.c b/main.c
index f4d646d..6af55e6 100644
--- a/main.c
+++ b/main.c
@@ -1,5 +1,6 @@
 #include <stdio.h>
 #include <math.h>
+
 #define BOT_SYMBOL 1
 #define OPPONENT_SYMBOL 2
 
@@ -9,7 +10,11 @@ short PATHS[8][3] = {
 	{0, 4, 8}, {2, 4, 6}
 };
 
-void reset(short* board){
+struct action{
+	short player;
+	short loc;
+};
+
 /*
 	Reset the game, clear the chessboard.
 	
@@ -19,11 +24,11 @@ void reset(short* board){
 	Results:
 		- None, set all blocks on the chessboard to zero. 
 */
+void reset(short* board){
 	for (short i=0; i<9; i++)
 		board[i] = 0;
 }
 
-void show(short *board){
 /*
 	Print the chessboard on the console.
 
@@ -33,6 +38,7 @@ void show(short *board){
 	Results:
 		- None. Only printing.
 */
+void show(short *board){
 	short loc;
 	printf("┼───┼───┼───┼\n");
 	for (short i=0; i<3; i++){
@@ -52,7 +58,6 @@ void show(short *board){
 	printf("\n\n");
 }
 
-void get_available_actions(short *board, short *result, short *length){
 /*
 	Save all available actions into the "result" array.
 
@@ -64,6 +69,7 @@ void get_available_actions(short *board, short *result, short *length){
 	Results:
 		- None. All available actions are saved into "result" and the number of actions is saved in "length"
 */
+void get_available_actions(short *board, short *result, short *length){
 	short index = 0;	
 	for (int i=0; i<9; i++)
 		if (board[i] == 0)
@@ -71,7 +77,6 @@ void get_available_actions(short *board, short *result, short *length){
 	*length = index;
 }
 
-short get_winner(short *board){
 /*
 	Return winner's number;
 
@@ -81,6 +86,7 @@ short get_winner(short *board){
 	Results:
 		- short winner_number(integer): winner's number, 0 for no winner now, 1 for Bot, 2 for opponent
 */
+short get_winner(short *board){
 	int a, b, c;
 	for (int i=0; i<8; i++){
 		a = PATHS[i][0]; b = PATHS[i][1]; c = PATHS[i][2];
@@ -91,7 +97,6 @@ short get_winner(short *board){
 	return 0;
 }
 
-int state_hash(short *board){
 /*
 	Hash chesstable's status into hash.
 	
@@ -101,6 +106,7 @@ int state_hash(short *board){
 	Results:
 		- int hash (integer): chessboard's status in i-th block * pow(3, i)
 */
+int state_hash(short *board){
 	int base, hash = 0;
 	for (int i=0; i<9; i++){
 		base = pow(3, i);
@@ -112,15 +118,39 @@ int state_hash(short *board){
 	return hash;
 }
 
-// void action(short *board, short a, )
+/*
+	Act on the chessboard.
+	
+	Args:
+		- short *board (array's address): chessboards' status
+		- struct action *a (a action's pointer): include player & choose loc
+		- int *state (pointer): for return. To save the chessboard's state hash which after doing this action
+		- int *reward (pointer): for return. To save the number of rewards which the player gets after doing this action.
+		- short *winner (pointer): for return. To save the winner in this action. If haven't finish, it will be zero.
+	
+	Results:
+		- None. Save in state & reward & winner
+*/
+void act(short *board, struct action *a, int *state, int *reward, short *winner){
+	board[a->loc] = a->player;
+	*winner = get_winner(board);
+	*state = state_hash(board);
+	if (*winner == a->player)
+		*reward = 1;
+	else if(*winner != 0)
+		*reward = -1;
+	else
+		*reward = 0;
+}
 
+// int choose_action
 
 int main(){
 	short board[9]= {0};			// tic tac toe's chessboard
 	short available_actions[9];
 	short available_actions_length;
 	short winner;
-	
+
 	board[1] = 2;
 	board[3] = 1;
 	board[4] = 1;