Click here to download moves.c.

/***************************************************
Write a program that allows the user to enter a
sequence of "moves" and prints out their position
after the moves.  Moves are:

left  - means a 90 deg counter clockwise turn (in place)
right - means a 90 deg clockwise turn (in place)
step  - means step forward 1 unit
stop  - terminates the sequence of moves.

The initial position is (0,0) facing North (up).
So the sequence "left step step left step right stop"
would leave you at (-2,-1).
***************************************************/
#include "si204.h"

int main() {
  // The direction is 0, 1, 2, or 3.
  // 0 indicates east, 1 is north, 2 is west, and 3 is south.

  // Initialize
  int x = 0;
  int y = 0;
  int direction = 1;
  cstring nextmove;

  // read in the first move
  fputs("Enter moves: ", stdout);
  readstring(nextmove, stdin);

  // Keep processing moves until "stop"
  while (strcmp(nextmove, "stop") != 0) {
    if (strcmp(nextmove, "left") == 0) {
      // turn left
      if (direction < 3) {
        direction = direction + 1;
      } else {
        direction = 0;
      }
    } else if (strcmp(nextmove, "right") == 0) {
      // turn right
      if (direction > 0) {
        direction = direction - 1;
      } else {
        direction = 3;
      }
    } else {
      // take a step in the current direction
      if (direction == 0) {
        x = x + 1;
      } else if (direction == 1) {
        y = y + 1;
      } else if (direction == 2) {
        x = x - 1;
      } else {
        y = y - 1;
      }
    }

    // Read next command
    readstring(nextmove, stdin);
  }

  // Print final position
  fputs("Final position is (", stdout);
  writenum(x, stdout);
  fputs(", ", stdout);
  writenum(y, stdout);
  fputs(")\n", stdout);

  return 0;
}