/*
    strings.c

	Jeff Ondich, 6 Jan 2022

    This program demonstrates the use of C strings (i.e. null-terminated
    char arrays), including a couple standard library string functions and
    passing strings as parameters to functions.
    
*/

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

#define BUFFER_SIZE 200

void reverse_string(char *string);

int main(int argc, char *argv[]) {
    // Parse the command line
    if (argc != 3) {
        fprintf(stderr, "Usage: %s string1 string2\n", argv[0]);
        return 1;
    }

    char *string1 = argv[1];
    char *string2 = argv[2];

    // Game 0: Build a null-terminated string manually
    printf("===== string game #0 =====\n");
    char buffer[BUFFER_SIZE];
    buffer[0] = 'd';
    buffer[1] = 'o';
    buffer[2] = 'g';
    //buffer[3] = '\0';
    printf("Here's your manually created string: \"%s\"\n", buffer);
    printf("\n");
    
    // Game 1: Report the lengths of the strings
    printf("===== string game #1 =====\n");
    printf("Length of \"%s\": %ld\n", string1, strlen(string1));
    printf("Length of \"%s\": %ld\n", string2, strlen(string2));
    printf("\n");

    // Game 2: Report the lengths of string1 manually
    printf("===== string game #2 =====\n");
    int length = 0;
    while (string1[length] != '\0') {
        length++;
    }
    printf("Length of \"%s\": %d\n", string1, length);
    printf("\n");

    // Game 3: Compare the strings
    printf("===== string game #3 =====\n");
    int comparison = strcmp(string1, string2);
    if (comparison < 0) {
        printf("\"%s\" comes before \"%s\".\n", string1, string2);
    } else if (comparison > 0) {
        printf("\"%s\" comes after \"%s\".\n", string1, string2);
    } else {
        printf("\"%s\" and \"%s\" are identical.\n", string1, string2);
    }
    printf("\n");

    // Game 4: concatenate the strings
    printf("===== string game #4 =====\n");
    strncpy(buffer, string1, BUFFER_SIZE);
    buffer[BUFFER_SIZE - 1] = '\0';
    strncat(buffer, string2, BUFFER_SIZE - 1);
    buffer[BUFFER_SIZE - 1] = '\0';
    printf("Your strings concatenated: \"%s\"\n", buffer);
    printf("\n");

    // Game 5: Reverse the result
    printf("===== string game #5 =====\n");
    reverse_string(buffer);
    printf("Your concatenated string, reversed: \"%s\"\n", buffer);
    printf("\n");

    return 0;
}

// Reverses the specified null-terminated string in-place.
void reverse_string(char *string) {
    int high_index = (int)(strlen(string)) - 1;
    int low_index = 0;
    while (low_index < high_index) {
        char saved_char = string[low_index];
        string[low_index] = string[high_index];
        string[high_index] = saved_char;
        low_index++;
        high_index--;
    }
}