While loop error in C++

[Reika]

Hey there, I posted once before with help and everyone did a good job guiding me.

I come now with another C++ question, using CodeWarrior 5
I'm making a tic tac toe game. The stage I am at now (there are three) is to make a human player vs. a computer player that moves randomly. (The next stage is with strategy)

However, I can't seem to figure out why it doesn't heed my loop to not place a random number over top a character that is already filled in. Here is the code:

void computerturn()
{
    char p1 = 'O';
    char p2 = 'X';
    int randnum;
 
    srand(time(0));
    randnum = rand()%9;
 
    while ((board[randnum] != p1) && (board[randnum] != p2))
    {
        srand(time(0));
        randnum = rand()%10;
 
        if ((board[randnum] != p1) && (board[randnum] != p2))
            board[randnum] = p2;
    }
}

So the focus is the function for the computer's turn. Is the problem in my loop conditions? What am I missing?

Thanks in advance!
~Reika

[AdrianH]

Hey there, I posted once before with help and everyone did a good job guiding me.

I come now with another C++ question, using CodeWarrior 5
I'm making a tic tac toe game. The stage I am at now (there are three) is to make a human player vs. a computer player that moves randomly. (The next stage is with strategy)

However, I can't seem to figure out why it doesn't heed my loop to not place a random number over top a character that is already filled in. Here is the code:

void computerturn()
{
    char p1 = 'O';
    char p2 = 'X';
    int randnum;
 
    srand(time(0));
    randnum = rand()%9;
 
    while ((board[randnum] != p1) && (board[randnum] != p2))
    {
        srand(time(0));
        randnum = rand()%10;
 
        if ((board[randnum] != p1) && (board[randnum] != p2))
            board[randnum] = p2;
    }
}

So the focus is the function for the computer's turn. Is the problem in my loop conditions? What am I missing?

Thanks in advance!
~Reika

There a few things I can comment on here.

• you don’t need to reseed every time you want to get a random number. You can, but I think (at least in this case) it is unnecessary.
• Your loop will never terminate.
  
  Tell me, what happens at line 10.
  
  Ok, now tell me what happens at line15-16 in that same iteration.
  
  Now tell me what happens when execution goes back to 10 again.
  
  
• line 13 doesn’t look right :nudge: :nudge: ;) ;) :cough: :cough: :hint: :hint:

Good luck,


Adrian

[Reika]

Hmmm.
Line 10 was meant to keep the loop running while the random number corresponded to a board space already taken by an 'X' or 'O'
I see now that it makes no sense.

Line 15-16 was meant to change the space the random number generated to an 'X' if it was not already occupied by an 'X' or an 'O'

I see now that these things overlap and are not really solving the problem.
I'll try and rework this out.

[AdrianH]

Hmmm.
Line 10 was meant to keep the loop running while the random number corresponded to a board space already taken by an 'X' or 'O'
I see now that it makes no sense.

Line 15-16 was meant to change the space the random number generated to an 'X' if it was not already occupied by an 'X' or an 'O'

I see now that these things overlap and are not really solving the problem.
I'll try and rework this out.

Personally, I'd skip the random value and put it to some single value that is a marker for 'not x or y'. It is easier to determine if nothing is occupying that spot.


Adrian

[Reika]

Personally, I'd skip the random value and put it to some single value that is a marker for 'not x or y'. It is easier to determine if nothing is occupying that spot.


Adrian

I need to have the random value, as the point of the project is to have the computer randomly select a spot to move to. The random number is that spot, but I need to make it not write over a space already there.

I changed my code to this:

void computerturn()
{
    char p1 = 'O';
    char p2 = 'X';
    int randnum;
 
    srand(time(0));
    randnum = rand()%9;
 
    if (board[randnum] == p1)
    {
        while (board[randnum] == p1)
        {
            srand(time(0));
            randnum = rand()%10;
 
            if (board[randnum] != p1)
                board[randnum] = p2;
        }
    }
    else if (board[randnum] == p2)
    {
        while (board[randnum] == p2)
        {
            srand(time(0));
            randnum = rand()%10;
 
            if (board[randnum] != p2)
                board[randnum] = p2;
        }
    }
    else
        board[randnum] = p2;
}

I had some very wierd problems with the random numbers, but now it works.... Only for a short while though. It'll stop the entire program randomly in the game before a winning condition is met (computer wins, tie, or human wins).

No error messages or anything, and I can't figure out the problem.
It may be that it has an error when the space it wants to move to is occupied...

[AdrianH]

I need to have the random value, as the point of the project is to have the computer randomly select a spot to move to. The random number is that spot, but I need to make it not write over a space already there.

If you have three values, X, Y and Unoccupied, it will not affect the chance of you overwriting that spot, and it is eaiser to determine if a spot is Unoccupied (only one test is preformed instead of two).

I changed my code to this:

void computerturn()
{
    char p1 = 'O';
    char p2 = 'X';
    int randnum;
 
    srand(time(0));
    randnum = rand()%9;
 
    if (board[randnum] == p1)
    {
        while (board[randnum] == p1)
        {
            srand(time(0));
            randnum = rand()%10;
 
            if (board[randnum] != p1)
                board[randnum] = p2;
        }
    }
    else if (board[randnum] == p2)
    {
        while (board[randnum] == p2)
        {
            srand(time(0));
            randnum = rand()%10;
 
            if (board[randnum] != p2)
                board[randnum] = p2;
        }
    }
    else
        board[randnum] = p2;
}

I had some very wierd problems with the random numbers, but now it works.... Only for a short while though. It'll stop the entire program randomly in the game before a winning condition is met (computer wins, tie, or human wins).

No error messages or anything, and I can't figure out the problem.
It may be that it has an error when the space it wants to move to is occupied...

*cough* *cough* line 26 & 15 *cough* *cough* ;)


Adrian