C++ Tic Tac Toe

#include <iostream>

using namespace std;

/*
 * print the game board
 *
 * this function is given and already complete
 * do NOT modify anything of it
 */
void printGameBoard(char s1, char s2, char s3, char s4, char s5, char s6, char s7, char s8, char s9)
{
    cout << "     |     |     " << endl;
    cout << "  " << s1 << "  |  " << s2 << "  |  " << s3 << endl;
    cout << "_____|_____|_____" << endl;
    cout << "     |     |     " << endl;
    cout << "  " << s4 << "  |  " << s5 << "  |  " << s6 << endl;
    cout << "_____|_____|_____" << endl;
    cout << "     |     |     " << endl;
    cout << "  " << s7 << "  |  " << s8 << "  |  " << s9 << endl;
    cout << "     |     |     " << endl << endl;
}

/*
 * print the message that asks the current player for his/her input
 *
 * you MUST call this function in your getValidInput implementation
 *
 * this function is given and already complete
 * do NOT modify anything of it
 */
void printQuestion(char currentPlayerSymbol)
{
     cout << "Player " << currentPlayerSymbol << ", please choose an unoccupied space (0 to quit): " << endl;
}

/*
 * return 'X' (uppercase English letter X) when roundNumber is odd
 * return 'O' (uppercase English letter O) otherwise
 *
 * complete the function body code, but do NOT modify the function prototype (including the function name, parameters, and return type)
 */
char getCurrentPlayerSymbol(int roundNumber)
{
    return (roundNumber%2)?'X':'O';
}

/*
 * return whether the input is valid
 * an input is valid if and only if the input is in the valid range of [0, 9]
 * and that the input refers to an unoccupied space (i.e. not 'O' and not 'X')
 *
 * be reminded to always return either true or false in all scenarios
 *
 * complete the function body code, but do NOT modify the function prototype (including the function name, parameters, and return type)
 */
bool isInputValid(int input, char s1, char s2, char s3, char s4, char s5, char s6, char s7, char s8, char s9)
{
    char tempGrid[] = {s1, s2, s3, s4, s5, s6, s7, s8 , s9};
    if(input >= 0 && input <= 9 && tempGrid[input-1] != 'X' && tempGrid[input-1] != 'O'){
        return true;
    }
}

/*
 * use some kind of loop to retrieve a valid integer input from the player, and return it at the end of the function
 * the flow is as follows
 * 1. Print exactly the question message "Player X, please choose an unoccupied space (0 to quit): "
 *    or "Player O, please choose an unoccupied space (0 to quit): " depending on what currentPlayerSymbol is,
 *    using the given printQuestion function
 * 2. Retrieve the integer input using cin
 * 3. If the input is valid (use the isInputValid function), return the input; if the input is invalid, go back to step 1
 *
 * *** IMPORTANT REQUIREMENT ***
 * you must NOT use any cout statement directly to print the question message in this function - you MUST call the given printQuestion function to print the message
 *
 * you can assume the player is sane and always inputs an integer (e.g. no alphabet/symbol input etc.)
 *
 * complete the function body code, but do NOT modify the function prototype (including the function name, parameters, and return type)
 */
int getValidInput(char currentPlayerSymbol, char s1, char s2, char s3, char s4, char s5, char s6, char s7, char s8, char s9)
{
    int userInput = -1;
    do{
        printQuestion(currentPlayerSymbol);
        cin >> userInput;
    }while(!isInputValid(userInput, s1, s2, s3, s4, s5, s6, s7, s8, s9));
    return userInput;
}

/*
 * put the currentPlayerSymbol to one of the s1, s2, ..., s9 variables according to the input which is guaranteed to be in the range of [1, 9]
 *
 * complete the function body code, but do NOT modify the function prototype (including the function name, parameters, and return type)
 */
void putSymbol(int input, char currentPlayerSymbol, char& s1, char& s2, char& s3, char& s4, char& s5, char& s6, char& s7, char& s8, char& s9)
{
    switch(input){
        case 1: s1 = currentPlayerSymbol;break;
        case 2: s2 = currentPlayerSymbol;break;
        case 3: s3 = currentPlayerSymbol;break;
        case 4: s4 = currentPlayerSymbol;break;
        case 5: s5 = currentPlayerSymbol;break;
        case 6: s6 = currentPlayerSymbol;break;
        case 7: s7 = currentPlayerSymbol;break;
        case 8: s8 = currentPlayerSymbol;break;
        case 9: s9 = currentPlayerSymbol;break;
    }
}

/*
 * return the game state
 * game state is 1 if player 1 (X) has won the game
 * game state is 2 if player 2 (O) has won the game
 * game state is -1 if the broad is full and no one has won the game yet (i.e. draw game)
 * game state is 0 otherwise
 *
 * complete the function body code, but do NOT modify the function prototype (including the function name, parameters, and return type)
 */
int getGameState(char s1, char s2, char s3, char s4, char s5, char s6, char s7, char s8, char s9)
{
    //Function Variables
    char tempGrid[] = {s1, s2, s3, s4, s5, s6, s7, s8 , s9};

    if (s1 == s2 && s2 == s3){
        return(s1=='X')?1:2;
    }
    else if(s4 == s5 && s5 == s6){
        return(s4=='X')?1:2;
    }
    else if(s7 == s8 && s8 == s9){
        return(s7=='X')?1:2;
    }
    else if(s1 == s4 && s4 == s7){
        return(s1=='X')?1:2;
    }
    else if(s2 == s5 && s5 == s8){
        return(s2=='X')?1:2;
    }
    else if(s3 == s6 && s6 == s9){
        return(s3=='X')?1:2;
    }
    else if(s1 == s5 && s5 == s9){
        return(s1=='X')?1:2;
    }
    else if(s3 == s5 && s5 == s7){
        return(s3=='X')?1:2;
    }
    for(int i = 0;i < 9; i++){
        if(tempGrid[i] != 'X' && tempGrid[i] !='O')
            return 0;
    }
    return -1;
}

/*
 * return whether the game is over
 * the game is over when the game is a draw game, or either of the players has won
 *
 * complete the function body code, but do NOT modify the function prototype (including the function name, parameters, and return type)
 */
bool isGameOver(char s1, char s2, char s3, char s4, char s5, char s6, char s7, char s8, char s9)
{
//Function Variables
    char tempGrid[] = {s1, s2, s3, s4, s5, s6, s7, s8 , s9};

    if (s1 == s2 && s2 == s3){
        return 1;
    }
    else if(s4 == s5 && s5 == s6){
        return 1;
    }
    else if(s7 == s8 && s8 == s9){
        return 1;
    }
    else if(s1 == s4 && s4 == s7){
        return 1;
    }
    else if(s2 == s5 && s5 == s8){
        return 1;
    }
    else if(s3 == s6 && s6 == s9){
        return 1;
    }
    else if(s1 == s5 && s5 == s9){
        return 1;
    }
    else if(s3 == s5 && s5 == s7){
        return 1;
    }
    for(int i = 0;i < 9; i++){
        if(tempGrid[i] != 'X' && tempGrid[i] !='O')
            return 0;
        cout << "i is " << i << endl;
        if(i == 8)
            return 1;
    }
}

/*
 * this is the main function
 *
 * this function is given and already complete
 * do NOT modify anything of it
 */
int main()
{
    char s1 = '1', s2 = '2', s3 = '3', s4 = '4', s5 = '5', s6 = '6', s7 = '7', s8 = '8', s9 = '9'; //variables that represent the 9 spaces in the game board
    int roundNumber = 1; //the round number, starts with 1
    int gameState = 0; //game state, refer to the getGameState function for a description

    while(!isGameOver(s1, s2, s3, s4, s5, s6, s7, s8, s9)) //keep going until the game is over
    {
        char currentPlayerSymbol = getCurrentPlayerSymbol(roundNumber); //player symbol is either 'X' or 'O', refer to the getCurrentPlayerSymbol function for a description

        //print the round number and game board
        cout << "Round " << roundNumber << ":" << endl << endl;
        printGameBoard(s1, s2, s3, s4, s5, s6, s7, s8, s9);
        //cin.get();
        //get a valid input
        int input = getValidInput(currentPlayerSymbol, s1, s2, s3, s4, s5, s6, s7, s8, s9);

        if(input == 0) //exit the program if input is 0
        {
            cout << endl << "Bye!" << endl;
            return 0;
        }
        else //put the current player symbol to the board otherwise
            putSymbol(input, currentPlayerSymbol, s1, s2, s3, s4, s5, s6, s7, s8, s9);

        //update the game state
        gameState = getGameState(s1, s2, s3, s4, s5, s6, s7, s8, s9);

        //increase the round number
        roundNumber++;

        cout << endl << endl;
    }

    //game is done at this point, show the result
    cout << "Final state:" << endl << endl;
    printGameBoard(s1, s2, s3, s4, s5, s6, s7, s8, s9);
    if(gameState == -1) cout << "Draw game! Whoops!" << endl;
    else cout << "Congratulations, player " << (gameState==1?'X':'O') << "! You won! Wow!" << endl;

    return 0;
}