Tortoise and the Hare Pointers - c

Question

I'm building a program that simulates the tortoise and the hare race. The way I'm doing it is I create a SIZE 70 array of '_' to simulate the racetrack. Then I create 2 pointers, char *harePtr and char *tortoisePtr, that point to elements in that array (each one starting at [0]) The elements in the array that the pointers point to I'm also trying to change to 'T' and 'H' to simulate their locations on the track.
From there I've algorithms developed to determine, based on a random number generator, the action each would take.
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define SIZE 70
enum winner {TORTOISE, HARE};
int raceRunner (char wRaceTrack[], void (*moveHare)(char *harePtr, int i), void (*moveTortoise)(char *tortoisePtr, int i));
void moveHare (char *harePtr, int i);
void moveTortoise ( char *tortoisePtr, int i);
int main() {
char racetrack [SIZE];
size_t i;
for (i = 0; i < SIZE; i++)
racetrack[i] = '_';
int winner;
winner = raceRunner(racetrack, moveHare, moveTortoise);
if (winner == 1)
printf("The hare won!");
if (winner == 2)
printf("The tortoise won!");
}
int raceRunner (char wRaceTrack[], void (*moveHare)(char *harePtr, int i), void (*moveTortoise)(char *tortoisePtr, int i)){
srand(time(NULL));
int move = 1 + rand() %10;
char *harePtr = wRaceTrack;
char *tortoisePtr = wRaceTrack;
size_t i;
for (i = 0; i < SIZE; i++)
printf("%c,", wRaceTrack[i]);
printf("\n\n");
moveHare(harePtr, move);
moveTortoise(tortoisePtr, move);
i = 0;
for (i = 0; i < SIZE; i++)
printf("%c,", wRaceTrack[i]);
printf("\n\n");
if (harePtr = tortoisePtr)
printf("OUCH! Damn tortoise bit the hare!\n\n");
if (harePtr[69])
return 1;
else if (tortoisePtr[69])
return 2;
else
raceRunner(wRaceTrack, moveHare, moveTortoise);
}
void moveHare ( char *harePtr, int i) {
if (i == 1) {
*harePtr = '_';
harePtr - 12;
*harePtr = 'H';
}
if (2 <= i <= 3) {
return;
}
if (4 <= i <= 5){
*harePtr = '_';
harePtr + 9;
*harePtr = 'H';
}
if (6 <= i <= 8) {
*harePtr = '_';
harePtr + 1;
*harePtr = 'H';
}
if (9 <= i <= 10) {
*harePtr = '_';
harePtr - 2;
*harePtr = 'H';
}
}
void moveTortoise ( char *tortoisePtr, int i) {
if (1 <= i <= 5) {
*tortoisePtr = '_';
tortoisePtr + 3;
*tortoisePtr = 'T';
}
if (6 <= i <= 7){
*tortoisePtr = '_';
tortoisePtr - 6;
*tortoisePtr = 'T';
}
if (8 <= i <= 1) {
*tortoisePtr = '_';
tortoisePtr + 1;
*tortoisePtr = 'T';
}
}
What I'm trying to do is to then first set their CURRENT position back to '_', then increment each pointer to move up or down along the array accordingly, depending on what the random generator comes up with, and change that value to 'T' or 'H'. First pointer that points to the last element in the array, [69], wins the race.
When I run the program however, it consistently produces the same result each time, without the hare marker making an appearance anywhere on the array. I'm positive this is because I've my pointers set up improperly, as I'm still trying to wrap my head around the whole concept. Is it not possible to set up pointers to the same array? Or am I accessing the array in the wrong way through incorrect use of * and &? I'm honestly lost when it comes to using those operands to properly integrate pointers with arrays, so any and all help is appreciated. Thank you!

Answer 1

In your code, There are many issues.
First,
harePtr - 12;
...
harePtr + 9;
...
tortoisePtr + 3;
etc. statements are essentially useless. They do not affect harePtr or tortoisePtr, as you might have thought. The result of the opration is lost, unless you collect the same in some variable.
You can make use of += or -= in this regard, to modify the LHS operand value.
Second
regarding the chaining of relational operators, like
if (1 <= i <= 5)
see this answer to find out why it surprises you. is logically wrong.
Third
In your code
if (harePtr = tortoisePtr) –
does not compare the values, instead assigns it. You need to use == for comparison.
Fourth
srand() is used to seed the random number generator. You need to call srand() only once from the main(). You may want to refer to the related answer.

Answer 2

First of all, subtracting a number from a pointer will return a new value, not modify the existing one. Use the -= and += operators to actually change something.
Secondly, randomly changing a pointer and then using it without first checking whether it is still inside the valid range means the operating system will bite your program long before either animal manages to bite the other.