/* This program demonstrates
 * 1. strcmp - with our own implementation
 * 2. arrays of c-strings - an introduction
 *
 * * A note on ASCII:
 * In C++, char is both an integer type and a character type. This is because
 * C++ stores a char as an integer but interprets it as a character when it is
 * printed.
 * Since the days of telegraph, we have had the American Standard Code for
 * Information Interchange (ASCII), which assigns a numeric (integer) value for
 * every character that can be typed in. We have a numeric equivalent for every
 * uppercase letter, lowercase letter, numeral character, special character,
 * whitespace, control characters, etc.
 * When we store a character in a char variable (or a spot in a C-String), we
 * actually store the ASCII value of the character.
 *
 * An array of chars is a C-String. We can treat it as a regular array
 * along with all the special properties that apply to C-strings alone
 * Naturally, we can extend this idea into an array of C-Strings, which is
 * an array of arrays of chars - a 2 dimensional array of chars.
 * Here, each array of chars (an entire row of the array) can be treated as
 * a CString. Then, we only need to specify the row for the array.
 * We can also refer to each character individually. Then, we need to specify
 * both the row and the column.
 */
#include<iostream>
#include<cstring>

using namespace std;

int stringCompare (char st1[], char st2[]);
int main() {
    char str[100];
    char str2[100];

    cout << "Enter 2 strings: ";
    cin.getline(str, 100);
    cin.getline(str2, 100);

    /* Lexicographic ordering:
     * space < numeral (0-9) < uppercase letters (A-Z) < lowercase letters (a-z)
     * Spongebob, Patrick -> Patrick is "first" P < S
     * Spongebob , patirck -> Spongebob is "first", S < p
     * Spongebob, 4atrick -> 4atrick is "first", numeral < letters
     * Spongebob, Sqiudward -> Spongebob is "first" S==S, p<q
     * Squid, Square -> Square is first, first 3 letters are the same, a < i
     * Squid, Squidward -> Squid is "first", all letters matched until "Squid" ran out of letters
     * Squid Squid -> strings are equal
     */

    cout << "Demonstrating strcmp for string comparison:\n";

    int diff = stringCompare(str, str2);
    if (diff < 0)
        cout << str << " was first" << endl;
    else if (diff > 0)
        cout << str2 << " was first" << endl;
    else cout << "The two strings were equal" << endl;

    cout << "Demonstrating our version of strcmp:\n";
    diff = stringCompare(str, str2);
    if (diff < 0)
        cout << str << " was first" << endl;
    else if (diff > 0)
        cout << str2 << " was first" << endl;
    else cout << "The two strings were equal" << endl;

    /* An array of C-strings is essentially a two dimensional array of chars, where
     * each "row" can be considered a CString on its own.
     * So, we can treat is like a 2D array of chars, and all concepts that apply to
     * 2D arrays in general still apply.
     * But, we can also use the 4 extra "features" we added to c-strings (direct initialization,
     * direct reads, direct prints and null termination) to each row of the 2D array.
     */
    char list[10][20] = {{'A','p','p','l','e'}, "strawberry"};
    cout<<"Access individual character: "<<list[0][3]<<endl;
    cout<<"Access each row as a c-string: "<< list[1]<<endl;

    // We can read each row using getline
    cout<<"Enter 4 items: ";
    for(int i=0; i<4; i++)
        cin.getline(list[i],20);

    cout<<"Formatted list:\n";
    for(int i=0; i<4; i++)
        cout<<i+1<<". "<<list[i]<<endl;


    return 0;
}
/* Function stringCompare - compares 2 strings in lexicographic order
 * 2 parameters - cstrings to be compared.
 * Returns int - first non-zero comparison value. 0 if strings are equal
 * Method: Iterate through strings, until one or both terminate
 * Compare (subtract ASCII values) of the corresponding characters. If non-zero, return it
 * Here, we replicate the strcmp function
 * When we compare strings, we try and figure out which string will be found
 * before the other string in lexicographic ordering.
 * lexicographic ordering is alphabetic ordering except for the following
 * numeral characters -> uppercase characters -> lowercase characters
 * This is because we compare the ASCII values.
 * strcmp(string1, string2)
 * string comparison moves through both strings one character at a time,
 * and subtracts the ASCII value of the character of the second string
 * from the character of the first string.
 * The moment it sees a non-zero result on the subtraction, it returns that
 * So, strcmp returns
 * value < 0 if the first string occurs before the second string
 * value > 0 if the second string occurs before the first string
 * 0 if the strings are exactly equal (including case, spaces, etc.)
 */

int stringCompare(char st1[], char st2[])
{
    int diff = 0;
    int i=0;
    int len1 = strlen(st1), len2 = strlen(st2);

    while( i< len1 && i <len2 && diff == 0)
    {
        diff = st1[i] - st2[i];
        i++;
    }

    if(diff == 0)
    {
        if(i == len2)
        {
            diff = st1[i];
        }
        if(i == len1)
        {
            diff = - st2[i];
        }
    }

    return diff;

}