Data commit

Task/Snake/C/snake.c

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+// Snake
+
+// The problem with implementing this task in C is, the language standard
+// does not cover some details essential for interactive games:
+// a nonblocking keyboard input, a positional console output,
+// a and millisecond-precision timer: these things are all system-dependent.
+
+// Therefore the program is split in two pieces, a system-independent
+// game logic, and a system-dependent UI, separated by a tiny API:
+char nonblocking_getch();
+void positional_putch(int x, int y, char ch);
+void millisecond_sleep(int n);
+void init_screen();
+void update_screen();
+void close_screen();
+
+// The implementation of a system-dependent part.
+// Requires POSIX IEEE 1003.1-2008 compliant system and ncurses library.
+#ifdef __linux__
+#define _POSIX_C_SOURCE 200809L
+#include <time.h> // nanosleep
+#include <ncurses.h> // getch, mvaddch, and others
+char nonblocking_getch() { return getch(); }
+void positional_putch(int x, int y, char ch) { mvaddch(x, y, ch); }
+void millisecond_sleep(int n) {
+	struct timespec t = { 0, n * 1000000 };
+	nanosleep(&t, 0);
+	// for older POSIX standards, consider usleep()
+}
+void update_screen() { refresh(); }
+void init_screen() {
+	initscr();
+	noecho();
+	cbreak();
+	nodelay(stdscr, TRUE);
+}
+void close_screen() { endwin(); }
+#endif
+
+// An implementation for some other system...
+#ifdef _WIN32
+#error "not implemented"
+#endif
+
+// The game logic, system-independent
+#include <time.h> // time
+#include <stdlib.h> // rand, srand
+
+#define w 80
+#define h 40
+
+int board[w * h];
+int head;
+enum Dir { N, E, S, W } dir;
+int quit;
+
+enum State { SPACE=0, FOOD=1, BORDER=2 };
+// negative values denote the snake (a negated time-to-live in given cell)
+
+// reduce a time-to-live, effectively erasing the tail
+void age() {
+        int i;
+	for(i = 0; i < w * h; ++i)
+		if(board[i] < 0)
+			++board[i];
+}
+
+// put a piece of food at random empty position
+void plant() {
+	int r;
+	do
+		r = rand() % (w * h);
+	while(board[r] != SPACE);
+	board[r] = FOOD;
+}
+
+// initialize the board, plant a very first food item
+void start(void) {
+        int i;
+	for(i = 0; i < w; ++i)
+		board[i] = board[i + (h - 1) * w] = BORDER;
+	for(i = 0; i < h; ++i)
+		board[i * w] = board[i * w + w - 1] = BORDER;
+	head = w * (h - 1 - h % 2) / 2; // screen center for any h
+	board[head] = -5;
+	dir = N;
+	quit = 0;
+	srand(time(0));
+	plant();
+}
+
+void step() {
+	int len = board[head];
+	switch(dir) {
+		case N: head -= w; break;
+		case S: head += w; break;
+		case W: --head; break;
+		case E: ++head; break;
+	}
+	switch(board[head]) {
+		case SPACE:
+			board[head] = len - 1; // keep in mind len is negative
+			age();
+			break;
+		case FOOD:
+			board[head] = len - 1;
+			plant();
+			break;
+		default:
+			quit = 1;
+	}
+}
+
+void show() {
+	const char * symbol = " @.";
+        int i;
+	for(i = 0; i < w * h; ++i)
+		positional_putch(i / w, i % w,
+			board[i] < 0 ? '#' : symbol[board[i]]);
+	update_screen();
+}
+
+int main (int argc, char * argv[]) {
+	init_screen();
+	start();
+	do {
+		show();
+		switch(nonblocking_getch()) {
+			case 'i': dir = N; break;
+			case 'j': dir = W; break;
+			case 'k': dir = S; break;
+			case 'l': dir = E; break;
+			case 'q': quit = 1; break;
+		}
+		step();
+		millisecond_sleep(100); // beware, this approach
+		// is not suitable for anything but toy projects like this
+	}
+	while(!quit);
+	millisecond_sleep(999);
+	close_screen();
+	return 0;
+}