/*
    pointers.c

    Jeff Ondich, 6 Jan 2022
    Modified by Tanya Amert for Fall 2024

    This program demonstrates some basic techniques using C pointers.
    The main() function consists of an odd collection of examples.

    Compile as usual:

        gcc -Wall -Werror -g -o pointers pointers.c

    Run with no command-line arguments:

        ./pointers
*/

#include <stdio.h>
#include <stdlib.h>

#define BUFFER_SIZE 100

// Forward declarations of useful functions
void swap_integers(int *a, int *b);
void fill_with_alphabets(char *buffer, int buffer_size, int number_of_alphabets);

// Demonstrates different ways of allocating and working with memory
int main(int argc, char *argv[])
{
    printf("===== game 1: passing parameters by address =====\n");
    int x = 62;
    int y = 35;
    printf("Before swap: x = %d, y = %d\n", x, y);
    swap_integers(&x, &y);
    printf("After swap: x = %d, y = %d\n", x, y);
    printf("\n");

    printf("===== game 2: statically allocated memory =====\n");
    char buffer[BUFFER_SIZE];
    fill_with_alphabets(buffer, BUFFER_SIZE, 3);
    printf("Here are 3 alphabets: %s\n", buffer);
    printf("\n");

    printf("===== game 3: dynamically allocated memory =====\n");
    char *other_buffer;
    other_buffer = (char *)malloc(BUFFER_SIZE * sizeof(char));
    fill_with_alphabets(other_buffer, BUFFER_SIZE, 3);
    printf("Here are 3 alphabets: %s\n", other_buffer);
    free(other_buffer);
    printf("\n");

    printf("===== game 4: array index arithmetic =====\n");
    char animal[BUFFER_SIZE] = "WARTHOG";
    printf("Before: %s\n", animal);
    char *pointer = (char *)(animal + 4);
    *pointer = 'D';
    printf("After: %s\n", animal);
    printf("\n");

    return 0;
}

/*
 * Swaps the values stored at the two locations provided.
 *
 * Parameters:
 *   - a: pointer to an integer (will get the value at b)
 *   - b: pointer to an integer (will get the value at a)
 *
 * Returns:
 *   - nothing; modifies the values stored in a and b
 */
void swap_integers(int *a, int *b)
{
    if (a != NULL && b != NULL)
    {
        int saved_integer = *a;
        *a = *b;
        *b = saved_integer;
    }
}

/*
 * Fills the buffer with at most number_of_alphabets sets of
 * the characters a-z, up to buffer_size.  The last character
 * is guaranteed to be a '\0', making the contents of buffer
 * a null-terminated string.
 *
 * Parameters:
 *   - buffer: the memory address of the buffer to fill
 *   - buffer_size: the maximum number of characters to fill
 *   - number_of_alphabets: the maximum number of rounds of a-z
 *
 * Returns:
 *   - nothing; modifies the contents of buffer
 */
void fill_with_alphabets(char *buffer, int buffer_size, int number_of_alphabets)
{
    if (buffer != NULL)
    {
        int j = 0;
        for (int k = 0; k < number_of_alphabets; k++)
        {
            for (char ch = 'a'; ch <= 'z'; ch++)
            {
                if (j + 1 < BUFFER_SIZE)
                {
                    buffer[j] = ch;
                    j++;
                }
            }
        }
        buffer[j] = '\0';
    }
}