Would you help me understand this code?

This is a discussion on Would you help me understand this code? within the C Programming forums, part of the General Programming Boards category; Please explain me each sentence in this code, Thanks. Code: #include <stdio.h> #include <stdlib.h> void swap(int *a, int *b) { ...

  1. #1
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    Would you help me understand this code?

    Please explain me each sentence in this code, Thanks.
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    void swap(int *a, int *b)
    {
        int c = *a;
        *a = *b;
        *b = c;
    }
    
    void draw(int board[3][3])
    {
        int i, j;
        printf("\n");
        for(i = 0; i < 3; i++)
            for(j = 0; j < 3; j++)
            {
                if(board[i][j] != 0)
                    printf(" |%d|", board[i][j]);
                else
                    printf(" | |");
                if(j == 2)
                    printf("\n ----------- \n");
            }            
    }
    
    int main()
    {
        int board[3][3], *p = (int*)board;
        int i, j, c, x, ei, ej;
        
        //initialization
        for(i = 0, c = 8; i < 3; i++)
            for(j = 0; j < 3; j++, c--)
                board[i][j] = c;
        board[ei = 2][ej = 2] = 0;
         
         // check move //
        c = 0;
        while(c < 8)
        {
            draw(board);
            printf(" Move ");
            x = getchar() - 49 + 1;
            if((x < 10) && (x > 0))
                printf("%d\n",x);
            else 
            {
                printf("bad move\n");
                continue;
            }
            
            if(ei > 0 && board[ei - 1][ej] == x)
            {
                swap(&board[ei][ej], &board[ei - 1][ej]);
                ei--;
            }
            else if(ei < 2 && board[ei + 1][ej] == x)
            {
                swap(&board[ei][ej], &board[ei + 1][ej]);
                ei++;
            }
            else if(ej > 0 && board[ei][ej - 1] == x)
            {
                swap(&board[ei][ej], &board[ei][ej - 1]);
                ej--;
            }
            else if(ej < 2 && board[ei][ej + 1] == x)
            {
                swap(&board[ei][ej], &board[ei][ej + 1]);
                ej++;
            }
            else 
            {
                printf("bad move\n");
                continue;
            }
            
            // check win //
            for(c = 0; c < 8; c++)
                if(p[c] != c + 1)
                    break;             
        }
        
        draw(board);
        printf("\n You Win!");
        getchar();
        return 0;
    }

  2. #2
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    Anyone?

  3. #3
    Dr Dipshi++ mike_g's Avatar
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    Dude do you seriously expect anyone to explain a hundred lines of code to you one by one? Maybe start by asking what part don't understand, then someone should explain.

  4. #4
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    Alright then,
    just explain me this part
    Code:
    int main()
    {
        int board[3][3], *p = (int*)board;
        int i, j, c, x, ei, ej;
        
        //initialization
        for(i = 0, c = 8; i < 3; i++)
            for(j = 0; j < 3; j++, c--)
                board[i][j] = c;
        board[ei = 2][ej = 2] = 0;
         
         // check move //
        c = 0;
        while(c < 8)
        {
            draw(board);
            printf(" Move ");
            x = getchar() - 49 + 1;
            if((x < 10) && (x > 0))
                printf("&#37;d\n",x);
            else 
            {
                printf("bad move\n");
                continue;
            }
            
            if(ei > 0 && board[ei - 1][ej] == x)
            {
                swap(&board[ei][ej], &board[ei - 1][ej]);
                ei--;
            }
            else if(ei < 2 && board[ei + 1][ej] == x)
            {
                swap(&board[ei][ej], &board[ei + 1][ej]);
                ei++;
            }
            else if(ej > 0 && board[ei][ej - 1] == x)
            {
                swap(&board[ei][ej], &board[ei][ej - 1]);
                ej--;
            }
            else if(ej < 2 && board[ei][ej + 1] == x)
            {
                swap(&board[ei][ej], &board[ei][ej + 1]);
                ej++;
            }
            else 
            {
                printf("bad move\n");
                continue;
            }
            
            // check win //
            for(c = 0; c < 8; c++)
                if(p[c] != c + 1)
                    break;             
        }
        
        draw(board);
        printf("\n You Win!");
        getchar();
        return 0;
    }

  5. #5
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    Homework? If so, pay attention in class. I just started learning and know some of what is going on. Just Study up seeing as I don't think anyone is going to tell you line by line.

  6. #6
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    Nope, these aren't my homework.
    I am on 9th grade, I study this by my own, through the internet (I bought a book on PHP tho :P ...finished reading it a year ago)
    Usually, in our school we start learning programming languages on the 10th grade.
    Started working with C some months ago.

    So if you can, explain me this.
    This code works so cool so I'd to know how it works.
    Last edited by eXeCuTeR; 10-26-2007 at 08:22 PM.

  7. #7
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    well, i dont think anyone is going to try to explain this to you just out of principle.
    this kind of falls into that no homework questions/do this for me area.
    not to be rude or anything, im just trying to give advice.
    honestly, if you want to find out what it means, i would start with the basics.
    theres a tutorial here if you want to learn it though.

    oh, and just for future reference, dont do this:
    Code:
    //initialization
        for(i = 0, c = 8; i < 3; i++)
            for(j = 0; j < 3; j++, c--)
                board[i][j] = c;
                    board[ei = 2][ej = 2] = 0;
    from what i understand, this is a bad way to initialize variables.
    and just looking at it, the code itself wouldnt work.
    'why?' you might ask?
    read the tutorial

  8. #8
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    It works perfectly mate, I just checked it.

  9. #9
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    checked it how?
    what compiler are you using?
    and if you just checked it, why do you want people to explain what it does?
    Last edited by MikeyIckey; 10-26-2007 at 08:39 PM. Reason: forgot something

  10. #10
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    I use Geany.

    I don't want people to explain me what it does, I want people to explain me the lines of this program, I can't understand it.

  11. #11
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    when you detect inflicted confusion say stop.

    if else.
    arrays.
    &&.
    multidimensional arrays.
    for loops.
    arithmetic.

  12. #12
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    No..
    My question is why did the author typed: board[ei - 1][ej] and not board[ei - 5265][ej].
    How can I explain.

    I don't understand why he typed this: if(ei > 0 && board[ei - 1][ej] == x) for example, and the other things.

  13. #13
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    ei > 0 is a range check. I think the other part is something to do with the game rules. what is the program for?

  14. #14
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    Run it, it's hard to explain.

  15. #15
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    Quote Originally Posted by eXeCuTeR View Post
    Run it, it's hard to explain.
    oh ok now I get it...

    ei, ej is where the current position is. and -1 is the offset that you are trying to move. the if else tree is for one of four possible moves.

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