C AI – Efficiently Creating Semi-Intelligent AI for Tic Tac Toe

basically I am attempting to make a a efficient/smallish C game of Tic-Tac-Toe. I have implemented everything other then the AI for the computer so far. my squares are basically structs in an array with an assigned value based on the square. For example

s[1].value = 1;

therefore it's a x, and then a value of 3 would be a o. My question is whats the best way to create a semi-decent game playing AI for my tic-tac-toe game? I don't really want to use minimax, since It's not what I need. So how do I avoid a a lot of if statments and make it more efficient.

Here is the rest of my code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

struct state{ // defined
    int state; // 0 is tie, 1 is user loss, 2 is user win, 3 is ongoing game
    int moves;
};

struct square{ // one square of the board
    int value; // 1 is x, 3 is o
    char sign; // no space used
};

struct square s[9]; //set up the struct
struct state gamestate = {0,0}; //nothing

void setUpGame(){ // setup the game
    int i = 0;
    for(i = 0; i < 9; i++){
        s[i].value = 0;
        s[i].sign = ' ';
    }
    gamestate.moves=0;
    printf("\nHi user! You're \"x\"! I'm \"o\"! Good Luck :)\n");
}

void displayBoard(){// displays the game board
    printf("\n %c | %c | %c\n", s[6].sign, s[7].sign, s[8].sign);
    printf("-----------\n");
    printf(" %c | %c | %c\n", s[3].sign, s[4].sign, s[5].sign);
    printf("-----------\n");
    printf(" %c | %c | %c\n\n", s[0].sign, s[1].sign, s[2].sign);
}

void getHumanMove(){ // get move from human
    int i;
    while(1){
        printf(">>:");
        char line[255]; // input the move to play
        fgets(line, sizeof(line), stdin);
            while(sscanf(line, "%d", &i) != 1) { //1 match of defined specifier on input line
            printf("Sorry, that's not a valid move!\n");
            fgets(line, sizeof(line), stdin);
        }
        if(s[i-1].value != 0){printf("Sorry, That moves already been taken!\n\n");continue;}
        break;
    }
    s[i-1].value = 1;
    s[i-1].sign = 'x';
    gamestate.moves++;
}

int sum(int x, int y, int z){return(x*y*z);}

void getCompMove(){ // get the move from the computer

}

void checkWinner(){ // check the winner
    int i;
    for(i = 6; i < 9; i++){ // check cols
        if((sum(s[i].value,s[i-3].value,s[i-6].value)) == 8){printf("The Winner is o!\n");gamestate.state=1;}
        if((sum(s[i].value,s[i-3].value,s[i-6].value)) == 1){printf("The Winner is x!\n");gamestate.state=2;}   
    }
    for(i = 0; i < 7; i+=3){ // check rows
        if((sum(s[i].value,s[i+1].value,s[i+2].value)) == 8){printf("The Winner is o!\n");gamestate.state=1;}
        if((sum(s[i].value,s[i+1].value,s[i+2].value)) == 1){printf("The Winner is x!\n");gamestate.state=2;}
    }
    if((sum(s[0].value,s[4].value,s[8].value)) == 8){printf("The Winner is o!\n");gamestate.state=1;}
    if((sum(s[0].value,s[4].value,s[8].value)) == 1){printf("The Winner is x!\n");gamestate.state=2;}
    if((sum(s[2].value,s[4].value,s[6].value)) == 8){printf("The Winner is o!\n");gamestate.state=1;}
    if((sum(s[2].value,s[4].value,s[6].value)) == 1){printf("The Winner is x!\n");gamestate.state=2;}
}

void playGame(){ // start playing the game
    gamestate.state = 3; //set-up the gamestate
    srand(time(NULL));
    int temp = (rand()%2) + 1;
    if(temp == 2){ // if two comp goes first
        temp = (rand()%2) + 1;
        if(temp == 2){
            s[4].value = 2; s[4].sign = 'o';
            gamestate.moves++;
        }else{
            s[2].value = 2; s[2].sign = 'o';
            gamestate.moves++;
        }
    } 
    displayBoard();
    while(gamestate.state == 3){
        if(gamestate.moves<10);
            getHumanMove();
        if(gamestate.moves<10);
            getCompMove();
        checkWinner();
        if(gamestate.state == 3 && gamestate.moves==9){
            printf("The game is a tie :p\n");
            break;
        }
        displayBoard();
    }
}

int main(int argc, const char *argv[]){
    printf("Welcome to Tic Tac Toe\nby The Elite Noob\nEnter 1-9 To play a move, standard numpad\n1 is bottom-left, 9 is top-right\n");
    while(1){ // while game is being played
        printf("\nPress 1 to play a new game, or any other number to exit;\n>>:");
        char line[255]; // input whether or not to play the game
        fgets(line, sizeof(line), stdin);
        int choice; // user's choice about playing or not   
        while(sscanf(line, "%d", &choice) != 1) { //1 match of defined specifier on input line
            printf("Sorry, that's not a valid option!\n");
            fgets(line, sizeof(line), stdin);
        }
        if(choice == 1){
            setUpGame(); // set's up the game
            playGame(); // Play a Game
        }else {break;} // exit the application
    }
    printf("\nThank's For playing!\nHave a good Day!\n");
    return 0;
}