/*
    pointers.c

	Jeff Ondich, 6 Jan 2022

    This program demonstrates some basic techniques using C pointers.
    main() 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)
*/

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

#define BUFFER_SIZE 100

void swap_integers(int *a, int *b);
void fill_with_alphabets(char *buffer, int buffer_size, int number_of_alphabets);

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 * sizeof(char));
    *pointer = 'D';
    printf("After: %s\n", animal);
    printf("\n");

    printf("===== game 5: string copy with pointer arithmetic =====\n");
    char creature[BUFFER_SIZE] = "capybara";
    char beast[BUFFER_SIZE] = "null beast";
    printf("Before copying: %s (creature), %s (beast)\n", creature, beast);
    char *source_pointer = creature;
    char *destination_pointer = beast;
    while (*source_pointer != '\0') {
        *destination_pointer = *source_pointer;
        destination_pointer++;
        source_pointer++;
    }
    *destination_pointer = '\0';
    printf("After copying: %s (creature), %s (beast)\n", creature, beast);
    printf("BUT WATCH OUT! DID THESE POINTERS OVERFLOW THE BUFFER? HOW WOULD WE KNOW?\n");
    printf("\n");

    printf("===== game 6: same as game 5, but with terse code like pros sometimes do it =====\n");
    strncpy(creature, "capybara", BUFFER_SIZE);
    strncpy(beast, "null beast", BUFFER_SIZE);
    printf("Before copying: %s (creature), %s (beast)\n", creature, beast);
    char *p = creature;
    char *q = beast;
    while (*p != '\0') {
        *q++ = *p++;
    }
    *q = '\0';
    printf("After copying: %s (creature), %s (beast)\n", creature, beast);
    printf("BUT WATCH OUT! DID THESE POINTERS OVERFLOW THE BUFFER? HOW WOULD WE KNOW?\n");
    printf("\n");

    return 0;
}

void swap_integers(int *a, int *b) {
    if (a != NULL && b != NULL) {
        int saved_integer = *a;
        *a = *b;
        *b = saved_integer;
    }
}

void fill_with_alphabets(char *buffer, int buffer_size, int number_of_alphabets) {
    if (buffer != NULL) {
        int j = 0;
        for (int k = 0; k < 3; k++) {
            for (char ch = 'a'; ch <= 'z'; ch++) {
                if (j + 1 < BUFFER_SIZE) {
                    buffer[j] = ch;
                    j++;
                }
            }
        }
        buffer[j] = '\0';
    }
}