/*
    pointers.c

    Jeff Ondich, 6 Jan 2022
    Modified by Tanya Amert for Fall 2023

    This program demonstrates some basic techniques using C pointers.
    The main() function consists of an odd collection of examples,
    best consumed with the guidance of the author (that is, I'll walk
    through this program and its intentions in class).

    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';
    }
}