May I use goto in such situation?

Question

I'd like to know, if using goto ok in such situation? Can you suggest better solution? I see the only one to make second while cicle but then it would be necessary to call "makeMove" two times.

void BoardView::startGame()
{
    int currStep=0;
    int x,y;
    while (board_->isWin()==none)
    {
        currStep++;
        show();
    wrong:
        std::cout << " Player " << (currStep%2==0 ? 1 : 2) << ": ";
        std::cin >> x;
        y=x%10;
        x/=10;
        if (!board_->makeMove(x,y,(currStep%2==0 ? cross : zero)))
        {
            std::cout << "Wrong move! Try again.\n";
            goto wrong;
        }
    }
}

@PlasmaHH A loop *and* a separate function. The input really needs to be factored out into a separate function. — James Kanze, Mar 12 '12 at 12:02
[I would only admit goto being used in 1 situation.](http://stackoverflow.com/questions/3339946/how-to-avoid-long-chain-of-frees-or-deletes-after-every-error-check-in-c/3339958#3339958) — karlphillip, Mar 12 '12 at 12:14
@karlphillip: that example is for C. Prefer RAII for cleaning up in C++. — stefaanv, Mar 12 '12 at 12:19
@JamesKanze It's just a simple program for self-education, I don't think it's really necessary to create another function for input. Function call will eat some recourses, so... — , Mar 12 '12 at 12:20
@Fippo If it's for self-education, it's even more important to do it right. — James Kanze, Mar 12 '12 at 12:25

score 4 · Accepted Answer · answered Mar 12 '12 at 11:56

4

Don't use goto. Use a while (true) loop and break out of it when you've made a successful move.

while (true) {
    std::cout << " Player " << (currStep%2==0 ? 1 : 2) << ": ";
    std::cin >> x;
    y=x%10;
    x/=10;
    if (board_->makeMove(x,y,(currStep%2==0 ? cross : zero)))
        break;
    std::cout << "Wrong move! Try again.\n";
}

answered Mar 12 '12 at 11:56

Fred Foo

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2

Which is, of course, just a `goto` hiding under another name. – James Kanze Mar 12 '12 at 12:01
4

@JamesKanze: yes, but one that jumps to end of a scope instead of some random place in the program. Besides, every control structure is a goto in disguise. – Fred Foo Mar 12 '12 at 12:02
But it doesn't correct the original problem, that he's trying to do too much in the function. – James Kanze Mar 12 '12 at 12:12

score 1 · Answer 2 · answered Mar 12 '12 at 11:59

Maybe:

void BoardView::startGame()
{
    int currStep=1;
    int x,y;
    show();
    while (board_->isWin()==none)
    {
        std::cout << " Player " << (currStep%2==0 ? 1 : 2) << ": ";
        std::cin >> x;
        y=x%10;
        x/=10;
        if (!board_->makeMove(x,y,(currStep%2==0 ? cross : zero)))
        {
            std::cout << "Wrong move! Try again.\n";
            continue;
        }
        ++currStep;
        show();
    }
}

It's not exactly the same, but it doesn't use goto.

score 1 · Answer 3 · answered Mar 12 '12 at 12:00

Yes, you are allowed to make such jump, although it is usually better to avoid goto. You could rewrite it like this for example:

void BoardView::startGame()
{
    int currStep=1;
    int x,y;
    show();
    while (board_->isWin()==none)
    {
        std::cout << " Player " << (currStep%2==0 ? 1 : 2) << ": ";
        std::cin >> x;
        y=x%10;
        x/=10;
        if (board_->makeMove(x,y,(currStep%2==0 ? cross : zero)))
        {
            currStep++;
            show();
        }
        else
        {
            std::cout << "Wrong move! Try again.\n";
        }
    }
}

score 1 · Answer 4 · answered Mar 12 '12 at 12:01

General Advice is to avoid GOTO statement, However, see the modified code with do while

    void BoardView::startGame()
{
    int currStep=0;
    int x,y;
    while (board_->isWin()==none) {

        currStep++;
        show();
        int retry = 0; /* So that 'retry' is visible to do while loop */ 
        do {
              retry = 0;
              std::cout << " Player " << (currStep%2==0 ? 1 : 2) << ": ";
              std::cin >> x;
              y=x%10;
              x/=10;
             if (!board_->makeMove(x,y,(currStep%2==0 ? cross : zero))) {

                std::cout << "Wrong move! Try again.\n";
                retry = 1
             } 

       } while (retry);
    }
}

score 0 · Answer 5 · answered Feb 05 '13 at 23:26

Two loops, no constant conditional expression, and only one call to makeMove:

void BoardView::startGameLoop()
{
    int currStep = 0;
    int x,y;
    while (none == board_->isWin())
    {
        ++currStep;
        show();

        for (;;)
        {
            std::cout << " Player " << ((currStep & 1) + 1) << ": ";
            std::cin >> x;
            y = x % 10;
            x /= 10;
            if (!board_->makeMove(x, y, (currStep & 1) ? zero : cross))
            {
                std::cout << "Wrong move! Try again.\n";
                continue;
            }
            break;
        }
    }
}

score 0 · Answer 6 · answered Mar 12 '12 at 12:02

you should avoid goto as much as you can.use only when using in large nested programs. otherwise use of goto makes the program unreliable,unreadable,and hard to debug. one more big problem with goto is that when we do use them we can never be sure how we got to certain point in our code.they obscure the flow of control. so avoid them.

I suggest use two while loops.... it will be better...

score 0 · Answer 7 · answered Mar 12 '12 at 12:10

What's wrong with:

std::pair<int, int> BoardView::getNextMove()
{
    std::cout << " Player " << (currStep & 2 == 0 ? 1 : 2) << ": ";
    int tmp;
    std::cin >> temp;
    return std::pair<int, int>( tmp / 10, tmp % 10 );
}

void BoardView::startGame() 
{
    int currentStep = 0;
    while ( myBoard->isWin() == none ) {
        std::pair<int, int> move = getNextMove();
        while ( ! myBoard->makeMove( move, (currentStep % 2 == 0 ?  cross : zero) ) {
            std::cout << "Wrong move! Try again" << std::endl;
            move = getNextMove();
        }
    }
}

(Although I'd prefer an explicit class for the Move type, rather than just std::pair. Members row and column are a lot more explicit than first and second.)

Usually, if you're tempted by a goto (or even a continue or a break), it's a symptom of putting too much in a single function.

I think you are ideologically right. But what about efficiency? Using pair, function call, returning value... — , Mar 12 '12 at 12:32
@Fippo What about efficiency? Is the code too slow? Has the profiler shown this to be the bottleneck. In practice, the most efficient code will be the most encapsulated code, since that will allow the most radical changes to the algorithms and the data structures once the bottlenecks are identified. — James Kanze, Mar 12 '12 at 13:46

May I use goto in such situation?

7 Answers7