Someone in this thread said I could ask for a review of my revision:
Ncurses Tic Tac Toe with simplistic AI

I re-wrote it from scratch using the suggestions from the answers. In particular I did the following:

1.) I got rid of Global Variables. For the few global constants I used #defines instead.

2.) I used arrays instead of lists of numbered variables, as suggested.

3.) Although it was not suggested I do so, I did improve the AI. This is the
main reason that it is not shorter I think.

There is one set of functions in particular that I think I could have combined into one function with a switch, during the AI Logic phase. I commented them so in the code and that's something I'd definitely like some
feedback on how to do.

I'd like to thank everyone in the previous thread for their tips and suggestions. There are some I did not follow, and for different reasons:

1.) I did not stop using rand() because it seems random enough for my
purposes. I did a test on my own using 10,000 attempts and checked how often
it picked each number between 0 and 99 and it was plenty random enough. So for this project I just kept using it. For those who still suggest I use a different random function, though, I am open to suggestions on how to best do that. I wouldn't mind making my OWN random function and would be stoked on tips for doing that. It's hard to imagine how I could improve even on rand()
though.

2.) I wanted to use Structs to immitate OOP for the tile spaces but could
not quite wrap my head around how to do so. In Python that kind of thing would be trivial but in C it's not easy for me to understand. Tips on how I could integrate Structs into this to get some kind of OOP would be really welcome.

Note on AI: I made it much tougher this time. It will beat a human player most of the time. It would beat a human every single time (ot tie) if I did not intentionally build in a "fart" function that causes it to fail a certain
percentage of the time.

Note on the code itself: Anyone who wants to use this for their own purposes is more than welcome. Although I am super proud of it I recognize that it is amateur stuff. If anyone wants to play some tic tac toe or can think of a use for this themselves they are more than welcome to it. It should compile pretty easily on most linux systems if you have ncurses.

Note on commenting: My comment style was a cause for concern from some of the reviewers in the other thread so I changed it up a bit. I fear it might be
too verbose but I wanted it to be easy for people who aren't too familiar with ncurses to follow along.

Note on Length: This is the real failing here. Although I implemented many of the suggestions from the other thread my code is actually longer... not shorter. There's at least one set of functions I can probably combine, but how else can I shorten it up?

As before, any and all comments and suggestions are welcome. I want to nail down a solid coding style with simple projects like this before moving on to
more complex projects in this language. Thank you! Without further ado, here is the code:

// tic tac toe v2 using suggestions from Stack Exchange for better style

// Minus the struct stuff which I don't quite understand just yet.



// ncurses for, well, ncurses

#include <ncurses.h>

// time for the random seed

#include <time.h>

// string.h for strlen() 

#include <string.h>

// stdlib and stdio because why not

#include <stdlib.h>

#include <stdio.h>

// ctype.h for toupper()

#include <ctype.h>



// #define's for the COLOR_PAIRs

#define X_COLOR 1

#define O_COLOR 2

#define BG_COLOR 3



// #defines used as a global constant

#define num_spaces 9



// Function Declarations

void init_spaces(char *space_ptr);

void paint_board(char playable_spaces[num_spaces]);

void take_turn(char side, char *space_ptr, char playable_spaces[num_spaces]);

void victory_splash(int game_over_state);

void paint_background();

void player_turn(char *space_ptr, char playable_spaces[num_spaces], char side);

void ai_turn(char *space_ptr, char playable_spaces[num_spaces], char side);

void set_color_ai_side(char ai_side);

void set_color_side(char side);

int main_menu();

int evaluate_board(char playable_spaces[num_spaces]);

int spaces_left(char playable_spaces[num_spaces]);

int ai_fart(const int chance_to_fart);

int pick_random_space(char playable_spaces[num_spaces]);

int check_for_winning_move(char playable_spaces[num_spaces], char ai_side);

int check_for_block(char playable_spaces[num_spaces], char side);

int check_for_2_space_path(char playable_spaces[num_spaces], char ai_side);

char pick_side();



int main(){

    // To-Do: Try the time(NULL) method for srand initialization and see if it works the same

    time_t t;

    srand((unsigned) time(&t));

    char playable_spaces[num_spaces] = {'X', 'X', 'X', 'X', 'X', 'X', 'X', 'X', 'X'};

    char *space_ptr = &playable_spaces[0];



    // Game over splash

    char game_over_str =  " Game Over! Any key to continue... ";

    char go_padding = "                                   ";

    int game_over_len = strlen(game_over_str);

    int row, col, x, y;



    //curses init

    initscr();

    cbreak();

    keypad(stdscr, 1);

    curs_set(0);

    start_color();

    init_pair(X_COLOR, COLOR_CYAN, COLOR_BLACK);

    init_pair(O_COLOR, COLOR_GREEN, COLOR_BLACK);

    init_pair(BG_COLOR, COLOR_YELLOW, COLOR_BLACK);

    noecho();



    // Main Menu outer loop

    int running = 1;

    while(running){

        curs_set(0);

        // Main menu function quits or continues

        running = main_menu();

        // In-Game inner loop

        if(running == 0){

            break;

        }

        int playing = 1;

        while(playing){

            // Init all spaces to blank

            init_spaces(space_ptr);

            // Player picks their side.

            char side = pick_side();

            // The inner, inner turn loop

            int turning = 1;

            while(turning){

                int game_over = 0;

                // Paint the board state as it is that turn

                paint_board(playable_spaces);

                // Function that governs the turn cycle

                take_turn(side, space_ptr, playable_spaces);

                // Evaluate the board for game over state

                game_over = evaluate_board(playable_spaces);

                if(game_over > 0){

                    // paint the board with a splash on game over

                    // so the player can evaluate the board for a moment

                    paint_board(playable_spaces);

                    getmaxyx(stdscr, row, col);

                    y = row / 2 + 6;

                    x = col / 2 - game_over_len / 2;

                    attron(COLOR_PAIR(BG_COLOR));

                    mvprintw(y++, x, go_padding);

                    mvprintw(y++, x, game_over_str);

                    mvprintw(y, x, go_padding);

                    refresh();

                    getch();

                    // call victory_splash with int game_over as a parameter

                    // 1 = X wins, 2 = O wins, 3 = Tie

                    victory_splash(game_over);

                    // Reset the turning and playing loops to effectively start over

                    turning = 0;

                    playing = 0;

                }

            }

        }

    }



    // end curses

    endwin();



    return 0;

}





void init_spaces(char *space_ptr){ 

    // init all the spaces to ' ';

    int i;

    for(i = 0; i < 9; i++){

        *space_ptr = ' ';

        space_ptr++;

    }

}



void paint_board(char playable_spaces[num_spaces]){

    // paint the board and the playable spaces

    clear();

    paint_background();

    char break_lines = " ------- ";

    char play_lines =  " | | | | ";

    char padding =     "         ";

    int row, col, x, y;

    getmaxyx(stdscr, row, col);

    y = row / 2 - 4;

    int len;

    len = strlen(padding);

    x = col / 2 - len / 2;

    int k;

    const int num_lines = 9;

    attron(COLOR_PAIR(BG_COLOR));

    for(k = 0; k < num_lines; k++){

        // Paint the board itself without the pieces

        if(k == 0 || k == num_lines - 1){

            mvprintw(y + k, x, padding);

        }else{

            if(k % 2 == 0){

                mvprintw(y + k, x, play_lines);

            }else{

                mvprintw(y + k, x, break_lines);

            }

        }

    }

    attroff(COLOR_PAIR(BG_COLOR));

    // insert Xs and Os:

    // First set the dynamic x and y coordinates based on terminal size

    int playable_x[num_spaces] = {x+2, x+4, x+6, x+2, x+4, x+6, x+2, x+4, x+6};

    int playable_y[num_spaces] = {y+2, y+2, y+2, y+4, y+4, y+4, y+6, y+6, y+6};

    for(k = 0; k < num_spaces; k++){

        // For each of the playable spaces, first set the color

        if(playable_spaces[k] == 'O'){

            attron(COLOR_PAIR(O_COLOR));        

        }else if(playable_spaces[k] == 'X'){

            attron(COLOR_PAIR(X_COLOR));

        }else{

            attron(COLOR_PAIR(BG_COLOR));

        }

        // then insert the char for that space into the proper spot on the terminal

        mvaddch(playable_y[k], playable_x[k], playable_spaces[k]);

    }

    // refresh the screen

    refresh();

}



void take_turn(char side, char *space_ptr, char playable_spaces[num_spaces]){

    // using "side" to determine the order, call the functions to play a whole turn

    if(side == 'X'){

        player_turn(space_ptr, playable_spaces, side);

        paint_board(playable_spaces);

        if(spaces_left(playable_spaces)){

            if(!(evaluate_board(playable_spaces))){

                ai_turn(space_ptr, playable_spaces, side);

                paint_board(playable_spaces);

            }

        }

    }else if(side == 'O'){

        ai_turn(space_ptr, playable_spaces, side);

        paint_board(playable_spaces);

        if(spaces_left(playable_spaces)){

            if(!(evaluate_board(playable_spaces))){

                player_turn(space_ptr, playable_spaces, side);

                paint_board(playable_spaces);

            }

        }

    }

}



int main_menu(){

    clear();

    // Takes user input and returns an int that quits or starts a game

    int row, col, x, y;

    char error_string = " Invalid Input! Any key to try again... ";

    int error_str_len = strlen(error_string);

    char str1 =      " NCURSES TIC TAC TOE (v2) ";

    char padding =   "                          ";

    char str2 =      "    (P)lay or (Q)uit?     ";

    int len = strlen(str1);

    paint_background();

    getmaxyx(stdscr, row, col);

    y = row / 2 - 2;

    x = col / 2 - len / 2;

    mvprintw(y++, x, padding);

    mvprintw(y++, x, str1);

    mvprintw(y++, x, padding);

    mvprintw(y++, x, str2);

    mvprintw(y++, x, padding);

    int input;

    refresh();

    // get user input and return it

    input = toupper(getch());

    if(input == 'P'){

        return 1;

    }else if(input == 'Q'){

        return 0;

    }else{

        // call the function again if the input is bad

        x = col / 2 - error_str_len / 2;

        mvprintw(++y, x, error_string);

        getch();

        main_menu();

    }

}



int evaluate_board(char playable_spaces[num_spaces]){

    // Evaluates the state of the playable spaces and either does nothing

    // or ends the game.

    // Check all the possible winning combinations:

    if(playable_spaces[0] == 'X' && playable_spaces[1] == 'X' && playable_spaces[2] == 'X'){

        return 1;

    }else if(playable_spaces[3] == 'X' && playable_spaces[4] == 'X' && playable_spaces[5] == 'X'){

        return 1;

    }else if(playable_spaces[6] == 'X' && playable_spaces[7] == 'X' && playable_spaces[8] == 'X'){

        return 1;

    }else if(playable_spaces[0] == 'X' && playable_spaces[3] == 'X' && playable_spaces[6] == 'X'){

        return 1;

    }else if(playable_spaces[1] == 'X' && playable_spaces[4] == 'X' && playable_spaces[7] == 'X'){

        return 1;

    }else if(playable_spaces[2] == 'X' && playable_spaces[5] == 'X' && playable_spaces[8] == 'X'){

        return 1;

    }else if(playable_spaces[0] == 'X' && playable_spaces[4] == 'X' && playable_spaces[8] == 'X'){

        return 1;

    }else if(playable_spaces[2] == 'X' && playable_spaces[4] == 'X' && playable_spaces[6] == 'X'){

        return 1;

    }else if(playable_spaces[0] == 'O' && playable_spaces[1] == 'O' && playable_spaces[2] == 'O'){

        return 2;

    }else if(playable_spaces[3] == 'O' && playable_spaces[4] == 'O' && playable_spaces[5] == 'O'){

        return 2;

    }else if(playable_spaces[6] == 'O' && playable_spaces[7] == 'O' && playable_spaces[8] == 'O'){

        return 2;

    }else if(playable_spaces[0] == 'O' && playable_spaces[3] == 'O' && playable_spaces[6] == 'O'){

        return 2;

    }else if(playable_spaces[1] == 'O' && playable_spaces[4] == 'O' && playable_spaces[7] == 'O'){

        return 2;

    }else if(playable_spaces[2] == 'O' && playable_spaces[5] == 'O' && playable_spaces[8] == 'O'){

        return 2;

    }else if(playable_spaces[0] == 'O' && playable_spaces[4] == 'O' && playable_spaces[8] == 'O'){

        return 2;

    }else if(playable_spaces[2] == 'O' && playable_spaces[4] == 'O' && playable_spaces[6] == 'O'){

        return 2;

    }else{

        // Check all spaces for a tie

        int hits = 0;

        int i;

        for(i = 0; i < num_spaces; i++){

            if(playable_spaces[i] != ' '){

                hits++;

            }

        }

        if(hits >= num_spaces){

            return 3;

        }else{

            return 0;

        }

    }

}



char pick_side(){

    // Takes user input and returns the chosen side

    clear();

    paint_background();

    int row, col, x, y;

    char str1 =    " Press 'X' for X, 'O' for O, or 'R' for random! ";

    char str2 =    "        Good choice! Any key to continue...     ";

    char padding = "                                                ";

    char err_str = "      Invalid input! Any key to continue...     ";

    int len = strlen(str1);

    getmaxyx(stdscr, row, col);

    y = row / 2 - 2;

    x = col / 2 - len / 2;

    mvprintw(y++, x, padding);

    mvprintw(y++, x, str1);

    mvprintw(y++, x, padding);

    int input;

    int pick;

    refresh();

    // Get user input for picking a side. 'R' is random.

    input = toupper(getch());

    if(input == 'X' || input == 'O'){

        mvprintw(y, x, str2);

        refresh();

        getch();

        return (char) input;

    }else if(input == 'R'){

        pick = rand() % 2;

        if(pick == 0){

            input = 'X';

        }else if(pick == 1){

            input = 'O';

        }

        mvprintw(y, x, str2);

        refresh();

        getch();

        return (char) input;

    }else{

        // Call the function again on bad input

        mvprintw(y, x, err_str);

        refresh();

        getch();

        pick_side();

    }

}



void victory_splash(int game_over_state){

    // Takes the game over state and creates a victory splash

    char padding = "                                   ";

    char *str1 =     "              X Wins!              ";

    char *str2 =     "              O Wins!              ";

    char str3 =    "         any key to continue...    ";

    char *str4 =     "             A tie game!           ";

    int len = strlen(padding);

    char *vic_pointer = NULL;

    // To avoid code duplication, use a pointer to pick the right string

    if(game_over_state == 1){

        vic_pointer = str1;

    }else if(game_over_state == 2){

        vic_pointer = str2;

    }else if(game_over_state == 3){

        vic_pointer = str4;

    }

    clear();

    paint_background();

    int row, col, x, y;

    getmaxyx(stdscr, row, col);

    y = row / 2 - 2;

    x = col / 2 - len / 2;

    mvprintw(y++, x, padding);

    mvprintw(y++, x, vic_pointer);

    mvprintw(y++, x, padding);

    mvprintw(y, x, str3);

    refresh();

    getch();

}



void paint_background(){

    // Paints an elaborate flashy background

    int row, col, x, y;

    int pick;

    getmaxyx(stdscr, row, col);

    for(y = 0; y <= row; y++){

        for(x = 0; x <= col; x++){

            pick = rand() % 3;

            if(pick == 0){

                attron(COLOR_PAIR(X_COLOR));

                mvprintw(y, x, "X");

                attroff(COLOR_PAIR(X_COLOR));

            }else if(pick == 1){

                attron(COLOR_PAIR(O_COLOR));

                mvprintw(y, x, "O");

                attroff(COLOR_PAIR(O_COLOR));

            }else if(pick == 2){

                attron(COLOR_PAIR(BG_COLOR));

                mvprintw(y, x, " ");

                attroff(COLOR_PAIR(BG_COLOR));

            }

        }

    }

    refresh();

}



void player_turn(char *space_ptr, char playable_spaces[num_spaces], char side){

    // Function for the player turn

    char padding =  "                                                ";

    char str1 =     "    Use arrow keys to move and 'P' to place!    ";

    char str2 =     "                   Good move!                   ";

    char str3 =     "                 Invalid input!                 ";

    char str4 =     "             You can't move that way!           ";

    char str5 =     "              Space already occupied!           ";

    int len = strlen(padding);

    int row, col, x, y;

    getmaxyx(stdscr, row, col);

    const int board_line_len = 9;

    const int board_lines = 9;

    y = row / 2 - board_line_len / 2;

    x = col / 2 - board_line_len / 2;

    // Use the same method of dynamically measuring where the spaces are at using

    // terminal size as in the paint_board() function.

    int playable_x[num_spaces] = {x+2, x+4, x+6, x+2, x+4, x+6, x+2, x+4, x+6};

    int playable_y[num_spaces] = {y+2, y+2, y+2, y+4, y+4, y+4, y+6, y+6, y+6};

    // The variables and mvprintw functions for the "info line"

    const int info_line_y = (row / 2 - board_lines / 2) + 10;

    const int info_line_x = col / 2 - len / 2;

    mvprintw(info_line_y - 1, info_line_x, padding);

    mvprintw(info_line_y, info_line_x, str1);

    mvprintw(info_line_y + 1, info_line_x, padding);

    // Using a loop and pointers to collect user input

    int moving = 1;

    int input;

    int *pos_x = &playable_x[0];

    int *pos_y = &playable_y[0];

    move(*pos_y, *pos_x);

    curs_set(1);

    refresh();

    while(moving){

        // For each movement key, if the move is valid, use pointer

        // arithmetic to mov pos_x and pos_y around.

        input = toupper(getch());

        if(input == KEY_UP){

            if(*pos_y != playable_y[0]){

                pos_y -= 3;

                move(*pos_y, *pos_x);

                refresh();

            }else{

                mvprintw(info_line_y, info_line_x, str4);

                move(*pos_y, *pos_x);

                refresh();

            }

        }else if(input == KEY_DOWN){

            if(*pos_y != playable_y[6]){

                pos_y += 3;

                move(*pos_y, *pos_x);

                refresh();

            }else{

                mvprintw(info_line_y, info_line_x, str4);

                move(*pos_y, *pos_x);

                refresh();

            }

        }else if(input == KEY_LEFT){

            if(*pos_x != playable_x[0]){

                pos_x -= 1;

                move(*pos_y, *pos_x);

                refresh();

            }else{

                mvprintw(info_line_y, info_line_x, str4);

                move(*pos_y, *pos_x);

                refresh();

            }

        }else if(input == KEY_RIGHT){

            if(*pos_x != playable_x[2]){

                pos_x += 1;

                move(*pos_y, *pos_x);

                refresh();

            }else{

                mvprintw(info_line_y, info_line_x, str4);

                move(*pos_y, *pos_x);

                refresh();

            }

        }else if(input == 'P'){

            // I wanted to use KEY_ENTER instead of 'P' but it would not work

            // for some reason. When the user presses 'P' it checks where the

            // cursor is and sets the space_ptr to the appropriate index in the

            // playable_spaces array.

            if(*pos_y == playable_y[0] && *pos_x == playable_x[0]){

                space_ptr = &playable_spaces[0];                

            }else if(*pos_y == playable_y[1] && *pos_x == playable_x[1]){

                space_ptr = &playable_spaces[1];

            }else if(*pos_y == playable_y[2] && *pos_x == playable_x[2]){

                space_ptr = &playable_spaces[2];

            }else if(*pos_y == playable_y[3] && *pos_x == playable_x[3]){

                space_ptr = &playable_spaces[3];

            }else if(*pos_y == playable_y[4] && *pos_x == playable_x[4]){

                space_ptr = &playable_spaces[4];

            }else if(*pos_y == playable_y[5] && *pos_x == playable_x[5]){

                space_ptr = &playable_spaces[5];

            }else if(*pos_y == playable_y[6] && *pos_x == playable_x[6]){

                space_ptr = &playable_spaces[6];

            }else if(*pos_y == playable_y[7] && *pos_x == playable_x[7]){

                space_ptr = &playable_spaces[7];

            }else if(*pos_y == playable_y[8] && *pos_x == playable_x[8]){

                space_ptr = &playable_spaces[8];

            }

            // Then checks to see if that space is empty.

            // If so it sets the color properly and then places the piece.

            if(*space_ptr == ' '){

                if(side == 'X'){

                    attron(COLOR_PAIR(X_COLOR));

                    mvaddch(*pos_y, *pos_x, 'X');

                    attron(COLOR_PAIR(BG_COLOR));

                    *space_ptr = 'X';

                }else if(side == 'O'){

                    attron(COLOR_PAIR(O_COLOR));

                    mvaddch(*pos_y, *pos_x, 'O');

                    attron(COLOR_PAIR(BG_COLOR));

                    *space_ptr = 'O';

                }

                refresh();

                moving = 0;

            }else{

                mvprintw(info_line_y, info_line_x, str5);

                move(*pos_y, *pos_x);

                refresh();

            }

        }else{

            mvprintw(info_line_y, info_line_x, str3);

            move(*pos_y, *pos_x);

            refresh();

        }

    }

}



//////////////////////////////////////////////////////////////////////////////////////

// Begin AI Logic ////////////////////////////////////////////////////////////////////

//////////////////////////////////////////////////////////////////////////////////////



void ai_turn(char *space_ptr, char playable_spaces[num_spaces], char side){

    // wrapper for the AI turn

    /*

        Note: Since it is easy to accidentally create an unbeatable AI for tic tac toe

              I am building into the AI the chance for it to not make the optimal move.

                    This intentional fuzziness will be built into the functions that check for

                    avaialable spaces. When they find an optimal move they may just decide

                    to return 0 anyway.



        P-Code:

        if center square not taken, take center square 70% of the time;

        else:

            if opponent about to win, block them 90% of the time;

            elif self about to win take winning spot 90% of the time;

            else pick a random open spot;

    */

    // The chances for the AI to blow a move

    const int chance_to_fart_big_move = 10;

    const int chance_to_fart_center = 30;

    // Picking the character for the AI to use in its calculations

    char ai_side;

    if(side == 'X'){

        ai_side = 'O';

    }else if(side == 'O'){

        ai_side = 'X';

    }

    // Check the board state with a few functions.

    // These all return 0 if FALSE and the number of a valid

    // index to move into if TRUE

    int can_block_opponent = check_for_block(playable_spaces, side);

    int can_winning_move = check_for_winning_move(playable_spaces, ai_side);

    // Flow through the decision making logic applying the functions and checking for a fart

    int thinking = 1;

    int picked_space;

    while(thinking){

        if(playable_spaces[4] == ' '){

            if(!(ai_fart(chance_to_fart_center))){

                picked_space = 4;

                thinking = 0;

                break;

            }

        }

        if(can_winning_move){

            if(!(ai_fart(chance_to_fart_big_move))){

                picked_space = can_winning_move;

                thinking = 0;

            }else{

                picked_space = pick_random_space(playable_spaces);

                thinking = 0;

            }

        }else if(can_block_opponent){

            if(!(ai_fart(chance_to_fart_big_move))){

                picked_space = can_block_opponent;

                thinking = 0;

            }else{

                picked_space = pick_random_space(playable_spaces);

                thinking = 0;

            }

        }else{

            picked_space = pick_random_space(playable_spaces);

            thinking = 0;

        }

    }

    space_ptr = &playable_spaces[picked_space];

    if(ai_side == 'X'){

        attron(COLOR_PAIR(X_COLOR));

    }else if(ai_side == 'O'){

        attron(COLOR_PAIR(O_COLOR));

    }

    *space_ptr = ai_side;

    attron(COLOR_PAIR(BG_COLOR));

}





int ai_fart(const int chance_to_fart){

    // Takes the fart chance and returns 1 if the AI blows the move, 0 otherwise

    int roll;

    roll = rand() % 100 + 1;

    if(roll < chance_to_fart){

        return 1;

    }else{

        return 0;

    }

}



int pick_random_space(char playable_spaces[num_spaces]){

    // Returns a random open space on the board

    int roll;

    int rolling = 1;

    int pick;

    while(rolling){

        roll = rand() % num_spaces;

        if(playable_spaces[roll] == ' '){

            pick = roll;

            rolling = 0;

        }else{

            continue;

        }

    }

    return pick;

}



int check_for_winning_move(char playable_spaces[num_spaces], char ai_side){

    // Checks to see if the AI can win the game with a final move and returns the

    // index of the valid move if TRUE, returns 0 if FALSE

    int space;

    int pick;

    int picked = 0;

    for(space = 0; space < num_spaces; space++){

        // For each space: Check to see if it is a potential winning space and if so

        // switch "picked" to 1 and set "pick" to the winning index

        switch(space){

            case(0):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[1] == ai_side && playable_spaces[2] == ai_side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[3] == ai_side && playable_spaces[6] == ai_side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[4] == ai_side && playable_spaces[8] == ai_side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(1):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[0] == ai_side && playable_spaces[2] == ai_side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[4] == ai_side && playable_spaces[7] == ai_side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(2):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[1] == ai_side && playable_spaces[0] == ai_side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[4] == ai_side && playable_spaces[6] == ai_side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[5] == ai_side && playable_spaces[8] == ai_side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(3):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[4] == ai_side && playable_spaces[5] == ai_side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[0] == ai_side && playable_spaces[6] == ai_side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(4):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[1] == ai_side && playable_spaces[7] == ai_side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[3] == ai_side && playable_spaces[5] == ai_side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[0] == ai_side && playable_spaces[8] == ai_side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[6] == ai_side && playable_spaces[2] == ai_side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(5):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[8] == ai_side && playable_spaces[2] == ai_side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[3] == ai_side && playable_spaces[4] == ai_side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(6):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[4] == ai_side && playable_spaces[2] == ai_side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[7] == ai_side && playable_spaces[8] == ai_side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[3] == ai_side && playable_spaces[0] == ai_side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(7):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[6] == ai_side && playable_spaces[8] == ai_side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[4] == ai_side && playable_spaces[1] == ai_side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(8):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[5] == ai_side && playable_spaces[2] == ai_side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[4] == ai_side && playable_spaces[0] == ai_side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[7] == ai_side && playable_spaces[6] == ai_side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

        }

    }

    // return winning index if any

    if(picked){

        return pick;

    }else{

        return 0;

    }

}



int check_for_block(char playable_spaces[num_spaces], char side){

    // Checks to see if the AI can block the player from winning the game with a final move

    // and returns the index of the valid move if TRUE, returns 0 if FALSE

    // Note: I am sure there is a way to combine this this function with the

    //  check_for_winning_move() function in order to avoid code duplication, probably using

    //  one more parameter as a switch of some kind. I'd be open to examples of how to do that.

    int space;

    int pick;

    int picked = 0;

    for(space = 0; space < num_spaces; space++){

        // For each space: Check to see if it is a potential winning space and if so

        // switch "picked" to 1 and set "pick" to the winning index

        switch(space){

            case(0):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[1] == side && playable_spaces[2] == side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[3] == side && playable_spaces[6] == side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[4] == side && playable_spaces[8] == side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(1):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[0] == side && playable_spaces[2] == side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[4] == side && playable_spaces[7] == side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(2):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[1] == side && playable_spaces[0] == side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[4] == side && playable_spaces[6] == side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[5] == side && playable_spaces[8] == side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(3):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[4] == side && playable_spaces[5] == side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[0] == side && playable_spaces[6] == side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(4):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[1] == side && playable_spaces[7] == side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[3] == side && playable_spaces[5] == side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[0] == side && playable_spaces[8] == side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[6] == side && playable_spaces[2] == side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(5):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[8] == side && playable_spaces[2] == side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[3] == side && playable_spaces[4] == side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(6):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[4] == side && playable_spaces[2] == side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[7] == side && playable_spaces[8] == side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[3] == side && playable_spaces[0] == side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(7):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[6] == side && playable_spaces[8] == side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[4] == side && playable_spaces[1] == side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

            case(8):

                if(playable_spaces[space] == ' '){

                    if(playable_spaces[5] == side && playable_spaces[2] == side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[4] == side && playable_spaces[0] == side){

                        pick = space;

                        picked = 1;

                    }else if(playable_spaces[7] == side && playable_spaces[6] == side){

                        pick = space;

                        picked = 1;

                    }

                }

                break;

        }

    }

    // return winning index if any

    if(picked){

        return pick;

    }else{

        return 0;

    }

}



///////////////////////////////////////////////////////////////////////////////////

// End AI Logic ///////////////////////////////////////////////////////////////////

///////////////////////////////////////////////////////////////////////////////////



int spaces_left(char playable_spaces[num_spaces]){

    // Returns 0 if no spaces left

    int hits = 0;

    int k;

    for(k = 0; k < num_spaces; k++){

        if(playable_spaces[k] == ' '){

        hits++;

        }

    }

    return hits;

}

Capitalize your defines

#define num_spaces 9

should have NUM_SPACES instead of num_spaces.

Identify your local functions

Tell the compiler when you don't intend to export functions to a different translation unit. Mark all of your functions static except main.

Const integral args aren't needed

This:

int ai_fart(const int chance_to_fart);

doesn't really need its argument made const. const is most often applied to pointer-type arguments to indicate that the value won't be changed, but for integral types, the caller's copy cannot be changed, so doing this has little value.

Use real booleans

There are several variables, including running and turning, that are int but should be boolean. Include stdbool.h for this purpose.

Don't separate declaration from initialization

You do this in several places:

int i;

for(i = 0; i < 9; i++){

    *space_ptr = ' ';

    space_ptr++;

}

// ...

int len;

len = strlen(padding);

// ...

int input;

input = toupper(getch());

Don't do this. Just use the syntax int input = toupper(getch());

Remove redundant else

Whenever you return in an if, the following code doesn't need an else. So delete else from code like this:

if(input == 'Q'){

    return 0;

}else{

// ...

This occurs many times throughout your code.

Use more loops

Computers are good at repetition. This:

int playable_x[num_spaces] = {x+2, x+4, x+6, x+2, x+4, x+6, x+2, x+4, x+6};

should not be initialized in a literal. Initialize it in a loop. The compiler will make the (usually right) decision as to whether the loop should be unrolled.

Similarly, in your evaluate_board function, you have highly repeated code that should be refactored into loops to check playable_spaces.

More code that needs to be a loop -

        if(*pos_y == playable_y[0] && *pos_x == playable_x[0]){

            space_ptr = &playable_spaces[0];    

        // ...            

Choose better variable names

Particularly for str1, str2, etc.

Don't repeat yourself

This block of code:

    if(input == KEY_UP){

        if(*pos_y != playable_y[0]){

            pos_y -= 3;

            move(*pos_y, *pos_x);

            refresh();

        }else{

            mvprintw(info_line_y, info_line_x, str4);

            move(*pos_y, *pos_x);

            refresh();

        }

is repeated nearly verbatim four times. You should put this into a function. The same goes for your cases in check_for_winning_move and check_for_block.