Thread: why can't I delete the last node of the linked list?

  1. #1
    Registered User
    Join Date
    Jul 2020
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    2

    why can't I delete the last node of the linked list?

    I wrote a snake game on linux with c and ncurses.
    The length of snake is automatically added after every move.
    why can't I delete the last node of the linked list?

    insert
    Code:
    #include<ncurses.h>
    #include<stdio.h>
    #include<stdlib.h>
    #include<time.h>
    
    #define LENGTH 40
    #define HEIGHT 40 
    #define SPACE 0
    #define BORDER 1
    #define SNAKE 2
    #define FOOD 3
    #define UP 4
    #define DOWN 5
    #define LEFT 6
    #define RIGHT 7
    typedef struct snake snake;
    typedef struct food food;
    int game_map[HEIGHT][LENGTH]={SPACE};
    int new_direction=UP;
    struct snake
    {
        int y,x;
        snake *next;
    };
    snake *head=NULL,*new_head=NULL,*n=NULL;
    struct food
    {
        int y,x;
    };
    food new_food;
    int dir;
    void init_game()
    {
        for(int i=0;i<LENGTH;i++)
            game_map[0][i]=game_map[HEIGHT-1][i]=BORDER;
        for(int i=1;i<(HEIGHT-1);i++)
            game_map[i][0]=game_map[i][LENGTH-1]=BORDER;
        new_food.y=5;
        new_food.x=5;
        head=malloc(sizeof(snake));
        head->y=head->x=10;
        head->next=NULL;
        srand(time(NULL));
    }
    
    int get_direction()
    {
        int new=getch();
        switch(new)
        {
            case KEY_UP:
                new_direction=UP;break;
            case KEY_DOWN:
                new_direction=DOWN;break;
            case KEY_LEFT:
                new_direction=LEFT;break;
            case KEY_RIGHT:
                new_direction=RIGHT;break;
            default:
                break;
        }
        return new_direction;
    }
    
    void snake_move(int dir)
    {
        new_head=malloc(sizeof(snake));
        new_head->next=head;
        switch(dir)
        {
            case UP:
                new_head->y=head->y-1;
                new_head->x=head->x;
                break;
            case DOWN:
                new_head->y=head->y+1;
                new_head->x=head->x;
                break;
            case LEFT:
                new_head->y=head->y;
                new_head->x=head->x-1;
                break;
            case RIGHT:
                new_head->y=head->y;
                new_head->x=head->x+1;
                break;
        }
        head=new_head;
        n=new_head->next;
        while(n->next!=NULL)
        {
            new_head=n;
            n=new_head->next;
        }
        if((head->y==new_food.y) && (head->x==new_food.x))    //eat a new food
        {
            new_food.y=rand()%(HEIGHT-2)+1;
            new_food.x=rand()%(LENGTH-2)+1;
        }
        else
        {
            new_head->next=NULL;
            free(n);
        }
    }
    
    void draw()
    {
    
        game_map[new_food.y][new_food.x]=FOOD;
        n=head;
        while(n!=NULL)
        {
            game_map[n->y][n->x]=SNAKE;
            n=n->next;
        }
        for(int i=0;i<LENGTH;i++)
            for(int j=0;j<HEIGHT;j++)
                switch(game_map[i][j])
                {
                    case BORDER:
                        mvprintw(i,j,"#");break;
                    case FOOD:
                        mvprintw(i,j,"O");break;
                    case SNAKE:
                        mvprintw(i,j,"*");break;
                }
        refresh();
    }
    
    int main(int argc,char *argv[])
    {
        noecho();
        init_game();    
        initscr();
        cbreak();
        keypad(stdscr,true);
        halfdelay(3);
        
        while(1)
        {
            dir=get_direction();
            snake_move(dir);
            draw();
            if(head->y==0 || head->y == HEIGHT-1 || head->x ==0 || head->x==HEIGHT-1)
                break;
        }
        getch();
        endwin();
        
    }

  2. #2
    and the hat of int overfl Salem's Avatar
    Join Date
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    Posts
    38,163
    Some thoughts.

    1. Having so many global variables makes it harder for you.

    2. A singly linked list makes it harder for you.

    3. Spreading bits of linked list code all over the place makes it harder for you.

    Code:
    typedef struct {
        int y,x;
    } pos_t;
    
    // each snake segment
    typedef struct segment
    {
        pos_t   position;
        struct segment *prev;
        struct segment *next;
    } segment_t;
    
    // a doubly linked list for the whole snake
    typedef struct {
        struct segment *head;
        struct segment *tail;
    } snake_t;
    Then you create linked list functions
    Code:
    void add_to_head(snake_t *snake, pos_t pos) {
    }
    void remove_tail(snake_t *snake) {
    }
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  3. #3
    Registered User
    Join Date
    Jul 2020
    Posts
    2
    Thank you

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