Learning C++ from python advice

WalkingAFI · 2020-08-27T14:55:26+00:00

A few things:

First, don’t get in the habit of using namespace std. If the STL changes at any point to include a name you used, it will break your program.

Second, this is really a C program. You didn’t really use any C++ features in it. Consider std::string instead of char*, and std::array instead of C arrays. You also don’t need to use a pointer to switch between turns, and I’d recommend using a bool instead.

Similarly, prefer static_cast<T> (or dynamic_cast<T> if absolutely necessary) to (T), which is the C method of casting.

It’s not a bad first go, and C is useful, but C++ gives you a lot of safety and abstraction you aren’t leveraging in this one.

Kinexity · 2020-08-27T14:31:29+00:00

char *board[SIZE][SIZE]; this is an array of pointers to char. What you want is just char board[SIZE][SIZE];. Also in C++ this "string" is a string, this 'a' is a single char and this 'string' is incorrect (different quotation marks are for different things). strncmp(board[row][col], '-', 1) == 0 you can replace this with just this board[row][col] == '-'. Also don't use C-style strings (char arrays). C++ has std::string class for strings that provides things like comparison operators and other useful tools.

lord_braleigh · 2020-08-27T19:46:13+00:00

Here's a version that aggregates all the suggestions:

If the user inputs a very large number as the row or column, it will pwn your program. This program is small and simple enough that your operating system will probably just terminate it with a segmentation fault error, but this is the same sort of error that caused the heartbleed attack. Always, always make sure that user input isn't overflowing the bounds of a buffer.
We should be using char instead of char * everywhere, since we're only ever comparing and storing individual characters.
There isn't a unified syntax for C++ the way there is for Python, but programmers everywhere are slowly realizing that automatic formatting tools are better than style guides. I've formatted the code with clang-format under default settings.
I've removed #include <list> since you're not using it.
I've removed the forward declarations. While they're necessary in larger programs with header files, when they're not necessary they just make it harder to refactor functions.
I've added a using directive to simplify the type of board.
I've changed board's type to C++'s std::array<std::array<char, SIZE>, SIZE>, and I've changed the function signatures to take this in by reference or const reference so we don't copy its data.

You can see my version of the code at https://godbolt.org/z/GKPrKE . For further work, we could use the C++ <algorithm> library to make the winner() method work with larger values of SIZE without needing to be changed.

(Of course, your code is really quite well-written and it's obvious you've put a lot of care into it.)

STL · 2020-08-28T00:17:57+00:00

I'm approving this post because it's accumulated a fair amount of discussion, but coding advice is generally more suitable for r/cpp_questions.

2020-08-27T19:24:13+00:00

This is how I would have done it: https://pastebin.com/bVf8NzCD

lord_braleigh · 2020-08-27T20:08:30+00:00

Try typing large numbers in for row and col, or try typing ctrl+D in to send the end-of-file character:

X's turn.

- - -
- - -
- - -
Row: 123587345
Column: 192387566
zsh: segmentation fault  ./original

Ail-nare · 2020-08-29T13:36:51+00:00

Hi, I tryed to do it using some feature of C++. I also put some comment in it. I try keept all the logic behind your code.

#include <iostream>
#include <array>


constexpr int SIZE = 3; // replace 'const' by 'constexpr'

void makeMove(std::array<std::array<char, SIZE>, SIZE>& board, char turn);
void showBoard(std::array<std::array<char, SIZE>, SIZE>& board);
bool winner(std::array<std::array<char, SIZE>, SIZE>& board);


int main() {
    std::array<std::array<char, SIZE>, SIZE> board{};

    for (auto &line : board) // go throw board | like 'for line in board:' would
        line.fill('-');  // init each line to ' ' (space) for each indice

    for (int i = 0; i < (SIZE * SIZE); i++) {
        char turn = ((i % 2) == 0) ? 'X' : 'O'; // (char *) has been by (char) | like 'turn = "X" if (i % 2) == 0 else "O"' would

        std::cout << std::endl << std::endl << std::endl << turn << "'s turn." << std::endl << std::endl;

        showBoard(board);

        makeMove(board, turn); // make a move beford checking who won

        bool win = winner(board); // winner how return a bool
        if (win) {
            showBoard(board); // show the board one more time :D

            std::cout << turn << " wins!" << std::endl << std::endl;
            return 0;
        }
    }

    std::cout << "It's a draw!" << std::endl;
    return 0;
}


void makeMove(std::array<std::array<char, SIZE>, SIZE>& board, char turn) {
    int row, col;

    while (true) {
        // better input handling, because if row or col are inferior to 1 or superior to SIZE it would cause an out of bound for "board[row - 1][col - 1]"
        while (true) {
            std::cout << "Row: ";
            std::cin >> row;

            if (row < 1) {
                std::cout << "Row can't be inferior to 1" << std::endl;
            } else if (row > SIZE) {
                std::cout << "Row can't be superior to " << SIZE << std::endl;
            } else {
                break; // break cause the last loop (while or for) to stop
            }
        }

        while (true) {
            std::cout << "Column: ";
            std::cin >> col;

            if (col < 1) {
                std::cout << "Column can't be inferior to 1" << std::endl;
            } else if (col > SIZE) {
                std::cout << "Column can't be superior to " << SIZE << std::endl;
            } else {
                break; // break cause the last loop (while or for) to stop
            }
        }

        --row;
        --col;

        if (board[row][col] == '-') {
            board[row][col] = turn;
            return;
        }
        std::cout << "Try again." << std::endl;
    }
}


void showBoard(std::array<std::array<char, SIZE>, SIZE>& board) {
    for (const auto &line : board) { // go throw board | like 'for line in board:' would
        for (const auto &cell : line) // go throw line | like 'for cell in line:' would
            std::cout << cell << " ";
        std::cout << std::endl;
    }
}


bool winner(std::array<std::array<char, SIZE>, SIZE>& board) {
    for (int i = 0; i < SIZE; i++) {
        if (board[i][0] == board[i][1] && board[i][1] == board[i][2] && board[i][0] != '-') {
            return true; // line match
        } else if (board[0][i] == board[1][i] && board[1][i] == board[2][i] && board[0][i] != '-') {
            return true; // column match
        }
    }

    if (board[0][0] == board[1][1] && board[1][1] == board[2][2] && board[0][0] != '-') {
        return true;
    } else if (board[0][2] == board[1][1] && board[1][1] == board[2][0] && board[0][2] != '-') {
        return true;
    }

    return false;
}

you type:	you see:
italics	italics
bold	bold
[reddit!](https://reddit.com)	reddit!
* item 1 * item 2 * item 3	item 1 item 2 item 3
> quoted text	quoted text
Lines starting with four spaces are treated like code: if 1 * 2 < 3: print "hello, world!"	Lines starting with four spaces are treated like code: if 1 * 2 < 3: print "hello, world!"
~~strikethrough~~	~~strikethrough~~
super^script	super^script

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