Snake game problems

[cudla100]

I am trying to write my own snake game(I am learning from http://www.cplusplus.com/articles/3U75fSEw/), but i encountered problems that I can´t just solve. For example: When snake eats apple the piece that is suppose to appear right next to it appears almost on the other side of playing board. Playing board is broken, because sometimes it shows game over even when it should not and many other problems.

#include <string>
#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <unistd.h>
#include <ctime>
#include <thread>
#include <future>
#include <ncurses.h>

struct piece
{
    char c;
    int x, y;
};

class Snake
{
public:
    piece* piecesofsnake;
    int length;
    Snake(int);
    ~Snake();
};
Snake::Snake(int length)
{
    this->length = length;
    piecesofsnake = new piece[this->length];
}
Snake::~Snake()
{
    delete[] piecesofsnake;
}

int genrandvalue(int valuemin, int valuemax)
{
    srand(time(0));
    for (int i = 0; i < 1000000; i++)
        rand();
    return rand() % (valuemax - valuemin + 1) + valuemin;
}

void drawfield(int fieldsizex, int fieldsizey, const Snake& snake, piece apple)
{
    system("clear");
    for (int i = 0; i < fieldsizex; i++)
        std::cout << "\u2014";
    std::cout << "\n\r";

    for (int i = 0; i < fieldsizey - 2; i++)
    {
        for (int j = 0; j < fieldsizex; j++)
        {
            bool snakepieceon = false;
            for (int id = 0; id < snake.length; id++)
            {
                if (i == snake.piecesofsnake[id].y && j == snake.piecesofsnake[id].x)
                {
                    if (snake.piecesofsnake[id].c == '0')
                    {
                        std::cout << snake.piecesofsnake[id].c;
                        snakepieceon = true;
                    }
                }
            }
            if (snakepieceon == false && j == 0 || j == fieldsizex - 1)
            {
                std::cout << "|";
            }
            else if (snakepieceon == false && i == apple.y && j == apple.x)
            {
                std::cout << apple.c;
            }
            else if (snakepieceon == false)
            {
                std::cout << ' ';
            }
        }
        std::cout << "\n\r";
    }

    for (int i = 0; i < fieldsizex; i++)
        std::cout << "\u2014";
    std::cout << std::endl;
}

void gameover(char& c)
{
    system("clear");
    std::cout << "Game over!" << std::endl;
    c = 'q';
}

void gamelogic(char& c, char previousmovement, int fieldsizex, int fieldsizey, Snake& snake, piece &apple)
{
    for (int i = 0; i < snake.length; i++) //I have no idea what I thought.
    {
        if (snake.piecesofsnake[0].y > 0 &&
            snake.piecesofsnake[0].y < fieldsizey-1 &&
            snake.piecesofsnake[0].x > 0 &&
            snake.piecesofsnake[0].x < fieldsizex-1)
        {
            switch (previousmovement)
            {
            case 'w':
            {
                snake.piecesofsnake[i].y--;
            }
            break;
            case 's':
            {
                snake.piecesofsnake[i].y++;
            }
            break;
            case 'a':
            {
                snake.piecesofsnake[i].x--;
            }
            break;
            case 'd':
            {
                snake.piecesofsnake[i].x++;
            }
            break;
            }
            switch (c)
            {
            case 'w':
            {
                if (previousmovement != 'w' && snake.piecesofsnake[1].y != snake.piecesofsnake[0].y + 1)
                {
                    snake.piecesofsnake[i].y--;
                }
            }
            break;

            case 's':
            {
                if (previousmovement != 's' && snake.piecesofsnake[1].y != snake.piecesofsnake[0].y - 1)
                {
                    snake.piecesofsnake[i].y++;
                }
            }
            break;

            case 'a':
            {
                if (previousmovement != 'a' && snake.piecesofsnake[1].x != snake.piecesofsnake[0].x + 1)
                {
                    snake.piecesofsnake[i].x--;
                }
            }
            break;

            case 'd':
            {
                if (previousmovement != 'w' && snake.piecesofsnake[1].x != snake.piecesofsnake[0].x - 1)
                {
                    snake.piecesofsnake[i].x++;
                }
            }
            break;
            }
        }
        else
        {
            gameover(c);
        }
        
    }

    if ((apple.x == snake.piecesofsnake[0].x) && (apple.y == snake.piecesofsnake[0].y))
    {
        int lastpiece;
        for (int i = snake.length; i >= 0; i--)
        {
            if (snake.piecesofsnake[i].c == '0')
            {
                lastpiece = i;
            }
        }
        snake.piecesofsnake[lastpiece + 1].c = '0';
        switch (previousmovement)
        {
        case 'w':
            snake.piecesofsnake[lastpiece + 1].y = snake.piecesofsnake[lastpiece].y + 1;
            break;
        case 'a':
            snake.piecesofsnake[lastpiece + 1].x = snake.piecesofsnake[lastpiece].x + 1;
            break;
        case 's':
            snake.piecesofsnake[lastpiece + 1].y = snake.piecesofsnake[lastpiece].y - 1;
            break;
        case 'd':
            snake.piecesofsnake[lastpiece + 1].x = snake.piecesofsnake[lastpiece].x - 1;
            break;
        }
        apple.x = genrandvalue(0, fieldsizex);
        apple.y = genrandvalue(0, fieldsizey);
    }
}

int main(int argc, char **argv)
{
    initscr(); //inicialization of ncurses
    noecho(); //getch form ncurses won't show letter on terminal
    cbreak(); //no buffer of letters fot getch()
    nodelay(stdscr, TRUE); //getch won't wait for user input

    int fieldsizex = 160 / 4;
    int fieldsizey = 90 / 4; //I know that characters haven't got same length.
    
    Snake snake((fieldsizex - 2) * (fieldsizey - 2));
    snake.piecesofsnake[0].c = '0';
    snake.piecesofsnake[0].x = fieldsizex / 2;
    snake.piecesofsnake[0].y = fieldsizey / 2;

    piece apple;
    apple.c = 'O';
    apple.x = genrandvalue(0, fieldsizex);
    apple.y = genrandvalue(0, fieldsizey);

    char c;
    char previousmovement;
    while ((c != 'q') && (c != 'Q'))
    {
        c = getch();
        gamelogic(c, previousmovement, fieldsizex, fieldsizey, snake, apple);
        drawfield(fieldsizex, fieldsizey, snake, apple);
        usleep(250000);
        if (c == 'w' || c == 'a' || c == 's' || c == 'd')
            previousmovement = c;
    }
    endwin();
    return 0;
}

P.S. I am sorry for my bad english.

[cudla100]

I also don't know how to make movement of whole snake.

[jonnin]

the classic snake game moves like this:
draw a new pixel (box, *, whatever) at the next location where the snake's head will move. Delete (clear, set black, whatever) the last pixel on the snake's tail.

something (time? eating something? I can't remember this one) makes the snake get bigger. When he grows, you draw the head update but don't delete the tail pixel, every time it grows. Eventually he becomes so big it is hard not to run into yourself which kills him.

If you start talking about the banana throwing apes, I am out of here.