C programming Pointer and String operations - c

Question

So I have an assignment where I need to change certain functions by substituting pointer operations for array operations, and by substituting string operations for character operations. Now I have a basic understanding of pointers, arrays, strings, etc. but I cant understand what it is I have to do, and how I should go about doing it. Here is the code:
#include <stdio.h>
#pragma warning(disable: 4996)
// This program exercises the operations of pointers and arrays
#define maxrow 50
#define maxcolumn 50
char maze[maxrow][maxcolumn]; // Define a static array of arrays of characters.
int lastrow = 0;
// Forward Declarations
#define triple(x) x % 3 == 0
void initialization(int, int);
void randommaze(int, int);
void printmaze(int, int);
void initialization(int r, int c) {
int i, j;
for (i = 0; i < r; i++){
maze[i][0] = 'X'; // add border
maze[i][c - 1] = 'X'; // add border
maze[i][c] = '\0'; // add string terminator
for (j = 1; j < c - 1; j++)
{
if ((i == 0) || (i == r - 1))
maze[i][j] = 'X'; // add border
else
maze[i][j] = ' '; // initialize with space
}
}
}
// Add 'X' into the maze at random positions
void randommaze(int r, int c) {
int i, j, d;
for (i = 1; i < r - 1; i++) {
for (j = 1; j < c - 2; j++) {
d = rand();
if (triple(d))
{
maze[i][j] = 'X';
}
}
}
i = rand() % (r - 2) + 1;
j = rand() % (c - 3) + 1;
maze[i][j] = 'S'; // define Starting point
do
{
i = rand() % (r - 2) + 1;
j = rand() % (c - 3) + 1;
} while (maze[i][j] == 'S');
maze[i][j] = 'G'; // define Goal point
}
// Print the maze
void printmaze(int r, int c) {
int i, j;
for (i = 0; i < r; i++) {
for (j = 0; j < c; j++)
printf("%c", maze[i][j]);
printf("\n");
}
}
void main() {
int row, column;
printf("Please enter two integers, which must be greater than 3 and less than maxrow and maxcolomn, respectively\n");
scanf("%d\n%d", &row, &column);
while ((row <= 3) || (column <= 3) || (row >= maxrow) || (column >= maxcolumn)) {
printf("both integers must be greater than 3. Row must be less than %d, and column less than %d. Please reenter\n", maxrow, maxcolumn);
scanf("%d\n%d", &row, &column);
}
initialization(row, column);
randommaze(row, column);
printmaze(row, column);
//encryptmaze(row, column);
//printmaze(row, column);
//decryptmaze(row, column);
//printmaze(row, column);
}
Here are the questions I am struggling on:
Rewrite the function randommaze(row, column) by substituting pointer operations for all array operations. You may not use indexed operation like maze[i][j], except getting the initial value of the pointer.
Rewrite the function printmaze(row, column) by substituting string operations for all character operations.
If someone could please explain to me what I should be doing and how I should be doing it I would really appreciate it. Thanks!

Answer 1

Question 2.:
An array can be used as a pointer to it's first member. So, for example, array[0] and *array return the same thing - the value of the first element of the array. Since arrays are contiguous blocks of memory, if you increment (or add an offset to) a pointer that's pointing to the beginning of an array, you point to the next element of the array. That means that array[1] and *(array + 1) are the same thing.
If you a have a for loop that iterates indexing an array, you could just as well write it using pointer increments. Example:
/* Loop indexing an array */
int my_array [10];
int i = 0;
for(; i < 10; ++i) {
my_array[i] = 0;
}
/* Loop by offsetting a pointer */
int my_array [10];
int i = 0;
int *ptr = my_array; /* Make it point to the first member of the array*/
for(; i < 10; ++i) [
*(ptr + i) = 0;
}
/* Looping by incrementing the pointer */
int my_array [10];
int *ptr = my_array; /* Make it point to the first member of the array */
int *end_ptr = my_array + 10; /* Make a pointer pointing to one past the end of the array */
for(; ptr != end; ++ptr) [
*ptr = 0;
}
All these code examples do the same thing. Assign 0 to all members of the array. If you a have a multidimensional array, just remember that it's still just a contiguous block of memory.
Question 3.:
This question is not so clear to me, so my interpretation of what you're expected to do may be a bit off, but since you're just using printf to print single chars, I'm guessing that you should use a function to output a single char instead. Something like putchar.
Hopefully, this will steer you in the right direction.

Answer 2

It sounds as though you are engaged in a data structures course. The first challenge is to build an array mapping function. For example:
int main(int argc, char **argv)
{
int values[20][40];
values[0][0] = 1;
values[10][10] = 20;
/* Let's print these two ways */
printf("0,0: %d 10,10: %d\n", values[0][0], values[10][10]);
printf("0,0: %d 10,10: %d\n", *((*values) + (sizeof(int) * 0) + sizeof(int) * 0)), *((*values) + (sizeof(int) * 10) + sizeof(int) * 10)));
}
What we are doing is obtaining the address of the very first byte of memory in the 2d array (*values) and then adding a raw number of bytes as an offset to it to locate the value from the "array" that we'd like to access.
One of the main points of an exercise like this is to show you how the language actually works under the hood. This his how array mapping functions work generally and can be used as the basis, for example, for a language or compiler design course later, in addition to fast implementations of far more complex memory structures.
As to the second piece, I'm not super clear on this since there are no actual "string" operations built into C. I'd need a bit more detail there.