Snake Game implementation in C - c

Question

I need some help with some homework. I am supposed to make a Snake Game by using mostly "basic" c, only simple concepts.
To explain my thought process: Controls are the usual WASD. The grid we re playing in is an array. Head is represented by '#' and the tail by "*". What I am trying to do is implement this thinking:
Get input from user, move the head. Check in 4 possible directions of head's initial position, find the " * ", move it to the initial position of the head. Repeat till all '*' have been moved.
Obviously, I am doing something wrong while checking and/or moving, but I cannot quite figure out what parts I am treating wrong and after 2 days I am stuck with this as my closest to working version. I know I have been looking at it for too long, but I cant afford to take more time with it as it needs to be turned in.
Here is my code. I hope my error is very obvious to "fresh eyes".
main:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
int main(int argc, char *argv[]){
//get size of grid from args
int size;
size = atoi(argv[1]);
while(size < 6){
printf("Please insert a number greater than 6 so the game is
playable\n");
scanf("%d\n", &size);
}
char grid[size][size];
int sx,sy; //coordinates of snake head
int length = 2; //length of tail (without head)
int score = 0;
sx = 1;
sy = size/2;
//generate empty grid
int x, y;
for (y = 0; y < size; ++y) {
for (x = 0; x < size; ++x) {
if (y == 0 || y == size - 1) {
grid[y][x] = '-';
} else if (x == 0 || x == size - 1) {
grid[y][x] = '|';
} else {
grid[y][x] = ' ';
}
}
}
//initialize snake position
grid[sx][sy] = '#';
grid[sx+1][sy] = '*';
grid[sx+2][sy] = '*';
grid[sx+3][sy-6] = 'X';//just to test if it works, will be generated
randomly
//print grid
printGrid(size, grid);
play(sx,sy,size,grid,&length);
printf("*********GAME OVER********** \n final score: %d\n", score);
}
play() function. Practically all of the game.
int play(int x, int y, int size, char grid[size][size], int length){
int x0,y0,x1,y1,x2,y2,valid;//x0,y0 = current, x1,y1 next to check,
//x2,y2 = move there x0,y0
char end,dir; //what did the head land on
int score = 0;
int checkl = 0;
while(1){
scanf("%c", &dir);
switch(dir){
//move head, change head coordinates
case 'w': end = grid[x-1][y];
grid[x-1][y] = grid[x][y];
grid[x][y] = ' ';
x0 = x;
y0 = y;
x--;
break;
case 's': end = grid[x+1][y];
grid[x+1][y] = grid[x][y];
grid[x][y] = ' ';
x0 = x;
y0 = y;
x++;
break;
case 'a': end = grid[x][y-1];
grid[x][y-1] = grid[x][y];
grid[x][y] = ' ';
x0 = x;
y0 = y;
y--;
break;
case 'd': end = grid[x][y+1];
grid[x][y+1] = grid[x][y];
grid[x][y] = ' ';
x0 = x;
y0 = y;
y++;
break;
}
if ((end == '-') | (end =='|') | (end == '*')){
break;
}
printf("POINT 1\n");
do{
check(x0,y0,&x1,&y1, size, grid);
move(x0,y0, x2,y2, size, grid);
//if(valid == 1){
x2 = x0;
y2 = y0;
x0 = x1;
y0 = y1;
//}
checkl++;
printf("POINT 2\n");
}while(checkl <= length);
printf("POINT 3\n");
if (end == 'X'){
grid[x1][y1] = '*';
length++;
score += 10;
}
clearScreen();
printGrid(size, grid);
}
return score;
}
check() function. Implements the "look for the next '*'" process
int check(int x0, int y0, int *x1, int *y1, int size, char grid[size]
[size]){
if (grid[x0][y0-1] == '*'){
*x1 = x0;
*y1 = y0-1;
return 1;
}
else if (grid[x0][y0+1] == '*'){
*x1 = x0;
*y1 = y0+1;
return 1;
}
else if (grid[x0-1][y0] == '*'){
*x1 = x0-1;
*y1 = y0;
return 1;
}
else if (grid[x0+1][y0] == '*'){
*x1 = x0+1;
*y1 = y0;
return 1;
}
else
return 0;
}
move(). Self-explanatory
void move(int x0, int y0, int x2, int y2, int size, char grid[size]
[size]){
grid[x2][y2] = grid[x0][y0];
grid[x0][y0] = ' ';
}
A function to clear the window
void clearScreen()
{
const char *CLEAR_SCREEN_ANSI = "\e[1;1H\e[2J";
write(STDOUT_FILENO, CLEAR_SCREEN_ANSI, 12);
}
PrintGrid. Also self explanatory, have it as a function for convenience
void printGrid(int size, char grid[size][size]){
int y,x;
for (y = 0; y < size; ++y) {
for (x = 0; x < size; ++x) {
printf("%c", grid[y][x]);
}
printf("\n");
}
}
I believe the error is either in check, move, and in the do-while condition with the length in play. However, as I said, with a lot of trial and error, I am still here.
All of this should be in one file, but i could not align it properly all together. Thanks for any help, very appreciated.
Edit: Edited part of the code out. Now what happens after running the code is: I get the grid and the snake. The head moves just fine, along with the first '" of the tail but the rest does not follow. When it "eats" an 'X', it grows the tail where it should, but the '' added disappears in the next move. Also, the score goes up 20 instead of 10 so for some reason it enters the if twice for one move. The movement of the head + the first '*' as well as the "game over" scenarios work as they should.

Answer 1

Tidbit: This is only 10 actual characters, not 12 because the \ characters don't count:
const char *CLEAR_SCREEN_ANSI = "\e[1;1H\e[2J";
Better is to let the compiler count for you:
void clearScreen()
{
static const char CLEAR_SCREEN_ANSI[] = "\e[1;1H\e[2J";
write(STDOUT_FILENO, CLEAR_SCREEN_ANSI, sizeof(CLEAR_SCREEN_ANSI)-1);
}
Note that CLEAR_SCREEN_ANSI is now an array, not a pointer, and the -1 is for the trailing NUL byte.

Answer 2

Aha:
if ((end == '-') | (end =='|') | (end == '*')){
The | are bitwise OR and you almost certainly mean logical OR ||:
if ((end == '-') || (end =='|') || (end == '*')){
Edit: They actually do the same thing in this case, but it's a common-enough error that it's worth fixing.
Hat tip to #Sami Kuhmonen

Answer 3

I've spent some time looking at this, and it's clear this is entirely about program logic and less about C, so that makes it a lot more difficult to dive into something unfamiliar (and without a real spec).
The general idea is that the program draws a square playing field with a three-part snake: an # for a head and two * for the body, and the keyboard lets you move the snake around on the field with awds keys. You can't move on top of yourself, you can't go past the walls, and you want to find the food at location marked with X.
I believe your approach was to look for * characters, but I am not sure how it could tell a * from the middle of the snake from one at the end, so my approach is to maintain an array of all the positions of the snake, and in the main function it's initialized:
int ysnake[4] = { 1, 2, 3, 4 };
int xsnake[4] = { 15, 15, 15, 16 };
plus an obvious function to draw the snake given the position array:
static void drawsnake(
int snakelen, int xsnake[snakelen], int ysnake[snakelen],
int size, char grid[size][size])
{
char snakechar = '#'; // start with snake head
for (int i = 0; i < snakelen; i++)
{
grid[ ysnake[i] ]
[ xsnake[i] ] = snakechar;
snakechar = '*'; // all the rest are tails
}
}
So now we have the play() function, and this required quite a bit of refactoring, but it works for me.
int play(
int snakelen, int xsnake[snakelen], int ysnake[snakelen],
int size, char grid[size][size])
{
int score = 0;
while (1)
{
char dir;
scanf ("%c", &dir);
int proposed_xhead = xsnake[0];
int proposed_yhead = ysnake[0];
switch (dir)
{
case 'w': // up
proposed_yhead--;
break;
case 's': // down
proposed_yhead++;
break;
case 'a': // left
proposed_xhead--;
break;
case 'd': // right
proposed_xhead++;
break;
default: // ignore this invalid char
continue;
}
// first make sure we didn't go off the edge of the field
if (proposed_yhead <= 0 || proposed_yhead >= (size-1)
|| proposed_xhead <= 0 || proposed_xhead >= (size-1))
{
// would head off the maze, LOSE
break;
}
const char char_at_proposed_head = grid[proposed_yhead][proposed_xhead];
// now make sure we're not bumping into ourself
if (char_at_proposed_head == '#' // we shouldn't ever be able to bump into our head
|| char_at_proposed_head == '*') // we bumped into our tail
{
break; // would run into ourself: LOSE
}
// NOW we know it's a legal move. Did we find the food?
if (char_at_proposed_head == 'X')
{
// found the food!
// update score, set new food, etc.
score += 10;
}
// blank out the former tail; we're about to lose that position
grid[ ysnake[ snakelen-1 ] ]
[ xsnake[ snakelen-1 ] ] = ' ';
// shift all items down in the array, dropping the last one
for (int i = snakelen-1; i > 0; i--)
{
xsnake[i] = xsnake[i-1];
ysnake[i] = ysnake[i-1];
}
xsnake[0] = proposed_xhead;
ysnake[0] = proposed_yhead;
drawsnake(snakelen, xsnake, ysnake, size, grid);
clearScreen ();
printGrid (size, grid);
}
return score;
}
There's a clear separation of duties, where the decoding of the direction key translates to a change in the snake's head position, then checking for out-of-bounds or running into yourself, and finding if you found the food.
Then we move the snake by shifting the entire array of positions: the tail element drops off and the new one shifts onto the front. Then we re-draw the snake with new positions.
The main function is the same as yours at the top to set up the grid, but the snake configuration and play looks like:
int main(int argc, argv)
{
...
int length = 4;
int ysnake[4] = { 1, 2, 3, 4 };
int xsnake[4] = { 15, 15, 15, 16 };
drawsnake(length, xsnake, ysnake, size, grid);
// Put the food somewhere
grid[sx + 3][sy - 6] = 'X'; //just to test if it works, will be generated randomly
printGrid (size, grid);
score = play(length, xsnake, ysnake, size, grid);
printf ("*********GAME OVER********** \n final score: %d\n", score);
}
I didn't really do anything meaningful with the score and have only barely tested it, but it does let the little guy slither around the screen, and it might be a bit easier to follow.
Good luck.