//* Usefullness of enumeration *
#include <stdio.h>
#include <string.h>


typedef enum direction {NORTH, EAST, SOUTH, WEST, NA} direction ;
// can be partially replaced by const int definitions:
// const int NORTH =0, EAST =1, SOUTH =2, WEST =3, NA =4;


// The function str_to_dir converts a string of characters to direction
void str_to_dir(const char name[], direction *D) {
    if (strcmp(name,"north")==0)            *D=NORTH;
    else if (strcmp(name,"n")==0)           *D=NORTH;
    else if (strcmp(name,"east")==0)        *D=EAST;
    else if (strcmp(name,"e")==0)           *D=EAST;
    else if (strcmp(name,"south")==0)       *D=SOUTH;
    else if (strcmp(name,"s")==0)           *D=SOUTH;
    else if (strcmp(name,"west")==0)        *D=WEST;
    else if (strcmp(name,"w")==0)           *D=WEST;
    else                                    *D=NA;
}

// The functions turnLeft and turnRight are examples of successor and predecessor functions
void turnRight(direction D, direction *newD) {
   if (D==NORTH)                            *newD=EAST;
    else if (D==EAST)                       *newD=SOUTH;
    else if (D==SOUTH)                      *newD=WEST;
    else if (D==WEST)                       *newD=NORTH;
    else                                    *newD=NA;
 }

void turnLeft(direction D, direction *newD) {
   if (D==NORTH)                            *newD=WEST;
    else if (D==EAST)                       *newD=NORTH;
    else if (D==SOUTH)                      *newD=EAST;
    else if (D==WEST)                       *newD=SOUTH;
    else                                    *newD=NA;
 }

// The function updatePosition updates the postion of the manipulator within limits
void updatePosition(direction D, int *x, int *y) {
    const int borderX=10, borderY=10;
    if (D==NORTH && *y<borderY)              (*y)++;
    else if (D==EAST && *x<borderX)          (*x)++;
    else if (D==SOUTH && *y>-borderY)        (*y)--;
    else if (D==WEST && *x>-borderX)         (*x)--;
    // else ; // noting
}


int main()
{
    int x=0, y=0;

    for (;;) {
        char command[80];
        direction D;

        do {
            printf("(%4d,%4d) > ", x, y);
            scanf("%s", &command);
        } while ( strlen(command)==0);

        str_to_dir(command, &D);
        if (D==NA)
            break;

        updatePosition(D, &x, &y);

    }

    return 0;
}