Thread: Turtle Graphics (debug help)

- Your main should take argc and argv not void.

Why? Either is equally acceptable.

http://faq.cprogramming.com/cgi-bin/...&id=1043284376

[edit] And why cast NULL? [/edit]

First off, thank you for the help and suggestions. I took many of them into account, and slapped myself on the head multiple times for using getchar() instead of scanf(). I have got everything to work perfectly now, and hopefully my code is also more readable. This was my toughest project yet, and I look forward to exploring much more.

There is one other (minor) issue though. When I compile my program, I am issued a compiler warning as seen below. Could anyone elaborate on that warning for me? It would be much appreciated, as I don't understand what is causing it.

Code:

jason@lappy:~/c$ cc turtle.c -o turtle
turtle.c: In function ‘doCommand’:
turtle.c:141: warning: passing argument 1 of ‘printFloor’ from incompatible pointer type

It is referencing this function call:

Code:

		case COMMAND_PRINT:
			printFloor(floor);
			break;

And here is my final, revised code:

Code:

/************************************************************
	Turtle Graphics: turtle.c (final rev.)

	Use 50x50 array initialized to zeros to simulate a floor.
	Turtle starts at 0,0 with pen up.  When pen is down, set
	array elements to 1.  Display asterisk wherever there is
	a 1, when program is complete.

	Command list:
		1     Pen up
		2     Pen down
		3     Turn right
		4     Turn left
		5,10  Move forward 10 spaces
		6     Print the array
		9     End of data (sentinel)
************************************************************/

#include <stdio.h>
#define ARRAYMAX 50    /* length and width of grid */
#define COMMANDMAX 20  /* max amount of program commands */
#define COMMAND_UP 1
#define COMMAND_DOWN 2
#define COMMAND_RIGHT 3
#define COMMAND_LEFT 4
#define COMMAND_MOVE 5
#define COMMAND_PRINT 6
#define COMMAND_END 9

enum Direction {NORTH, EAST, SOUTH, WEST};
enum Status {UP, DOWN};

int readProg(int prog[][2], const int max);
int getCommand(int buffer[]);
void doCommand(const int command, const int arg, int floor[][ARRAYMAX]);
void printFloor(const int floor[][ARRAYMAX]);

enum Direction dir = NORTH;  /* direction turtle is facing */
enum Status stat = UP;       /* status of the pen          */
int turtlePosX = 0;          /* x-coord of turtle          */
int turtlePosY = 0;          /* y-coord of turtle          */

int main(void)
{
	int floor[ARRAYMAX][ARRAYMAX] = {{0}, {0}};  /* grid to print */
	int prog[COMMANDMAX][2] = {{0}, {0}};        /* instructions  */
	int commands = 0;        /* number of commands in the program */
	int i = 0;
	
	commands = readProg(prog, COMMANDMAX);
	
	while (i < commands) {   /* process the instructions */
		doCommand(prog[i][0], prog[i][1], floor);
		i++;
	}
	
	return 0;
}

/* Read the entire set of instructions into array prog[][] */
int readProg(int prog[][2], const int max)
{
	int buffer[2];
	int i = 0;
	
	while (i < max && getCommand(buffer)) {  /* process until sentinel */
		prog[i][0] = buffer[0];  /* transfer valid command into program */
		prog[i][1] = buffer[1];  /* transfer argument into program      */
		i++;
	}
	
	return i;  /* amount of commands, minus sentinel */
}

/* Read a single instruction from input */
int getCommand(int buffer[])
{
	scanf("%d,%d", &buffer[0], &buffer[1]);  /* read command to buffer */
	
	if (buffer[0] != COMMAND_MOVE)  /* set argument to 0 for any */
		buffer[1] = 0;               /* command except move */
	
	if (buffer[0] == COMMAND_END)
		return 0;
	else
		return 1;
}

/* Process a command onto the floor array */
void doCommand(const int command, const int arg, int floor[][ARRAYMAX])
{
	int i;
	
	switch(command) {
		case COMMAND_UP:
			stat = UP;
			break;
		case COMMAND_DOWN:
			stat = DOWN;
			floor[turtlePosX][turtlePosY] = 1;  /* activate current loc */
			break;
		case COMMAND_RIGHT:
			if (dir == WEST)
				dir = NORTH;
			else
				dir += 1;
			break;
		case COMMAND_LEFT:
			if (dir == NORTH)
				dir = WEST;
			else
				dir -= 1;
			break;
		case COMMAND_MOVE:
			if (dir == NORTH)
				for (i = 1; i <= arg; i++) {
					turtlePosY++;
					if (stat == DOWN)
						floor[turtlePosX][turtlePosY] = 1;
				}
			else if (dir == EAST)
				for (i = 1; i <= arg; i++) {
					turtlePosX++;
					if (stat == DOWN)
						floor[turtlePosX][turtlePosY] = 1;
				}
			else if (dir == SOUTH)
				for (i = 1; i <= arg; i++) {
					turtlePosY--;
					if (stat == DOWN)
						floor[turtlePosX][turtlePosY] = 1;
				}
			else if (dir == WEST)
				for (i = 1; i <= arg; i++) {
					turtlePosX--;
					if (stat == DOWN)
						floor[turtlePosX][turtlePosY] = 1;
				}
			break;
		case COMMAND_PRINT:
			printFloor(floor);
			break;
		default:
			break;
	}
}

/* Print the entire array to output.  0,0 will be lower left corner */
void printFloor(const int floor[][ARRAYMAX])
{
	int i,j;
	
	printf("\n");
	for (i = ARRAYMAX - 1; i >= 0; i--) {     /* in each row...     */
		for (j = 0; j <= ARRAYMAX - 1; j++) {  /* for each column... */
			if (floor[j][i] == 1)        /* print '*' if activated... */
				printf("*");
			else                         /* and a blank if not        */
				printf(" ");
		}
		printf("\n");  /* print a newline after the last column */
	}
}

And for the output:

Code:

jason@lappy:~/c$ ./turtle
2
5,15
3
5,15
3
5,15
3
5,15
1
6
9



































****************
*              *
*              *
*              *
*              *
*              *
*              *
*              *
*              *
*              *
*              *
*              *
*              *
*              *
*              *
****************
jason@lappy:~/c$

You're passing this:

Code:

int floor[][ARRAYMAX]

to this:

Code:

const int floor[][ARRAYMAX]

You can't really have const pointers to pointers. I can't explain why very coherently; try searching google or looking up in your book "const pointer".

Will do...thanks again.

The only reason I made it const in the first place, was the book stresses the "principle of least privilege". That is, not giving a function the ability to modify something unless it actually needs to. That was also the reason for prototyping functions inside other functions in my original version -- to only give that one function the ability to call it. (And yes, I do realize I violated that principle with the global vars. I may revisit that in the future.)

For reference, the book is "C How to Program" by Deitel. It starts with C, then gets into some C++ and touches on Java. I am partway through the chapter covering pointers, so hopefully things will become more clear shortly.