/*
Write a function that takes a C string as an input parameter and reverses the string. 
The function should use two local pointers, front and rear. The front pointer should 
initially reference the first character in the string, and the rear pointer should 
initially reference the last character in the string. Reverse the string by swapping 
the characters referenced by front and rear, then increment front to point to the 
next character and decrement rear to point to the preceding character, and so on, 
until the entire string is reversed. Write a main program to test your function 
on various strings of both even and odd length. 
*/

#include <iostream>
#include <cstring>
using namespace::std;

void reverse(char *);

void main()
{
	//  RUN YOUR PROGRAM AT LEAST 3 TIMES TO TEST
	//     A C++ string with exactly 1 char
	//     A C++ string with an even number of characters
	//     A C++ string with an odd number of characters
	//  COPY AND PASTE THE OUTPUT OF EACH RUN AS A COMMENT
	//     AT THE END OF THIS FILE

	const int SIZE = 101;

	// declare a char array of 101 characters
	char charArray[SIZE];

	cout << "This programs takes a C string as input, reverses characters,\n"
		<< "then prints the result.\n";
	
	// prompt the user to enter a char array with no spaces
	cout << "Enter characters from keyboard, except space or line breaks.\n";
	cout << "Press Enter when complete. >" << SIZE - 1 << " characters are truncated.\n";
	cin >> charArray;

	// Ensure last index is null value for C-string
	charArray[SIZE - 1] = '\0';

	// echo the data the user typed in
	cout << "\nYou entered:\n" << charArray << endl;

	// call the reverse function
	reverse(charArray);

	// display the char array after the function reverse has been called
	cout << "\nYour input reversed:\n" << charArray << endl;

	return;
}

// ======================
// reverse:
// Reverses the input string using pointers.
// ======================
void reverse(char *s)
{
	// write the code for the reverse function using pointers
	//      you cannot use array notation

	char *front, *rear, *tempThenNull;
	int cStringSize = strlen(s);
	
	front = s;
	rear = s + (cStringSize - 1); // NOTE: s+(cStringSize) is '\0' value.
	tempThenNull = s + (cStringSize); // temporary pointer to NULL '\0' that I'll clobber then reset
	
	for (int i = 0; i < (cStringSize/2); i++)
	{
		*tempThenNull = *(front + i);
		*(front + i) = *(rear - i);
		*(rear - i) = *tempThenNull;

		// Line of code for testing only.
		//cout << "*(front+" << i << ")=" << *(front+i) << " *(rear+" << i << ")=" << *(rear+i) << endl;
	}

	// reset temporary pointer back to NULL
	*tempThenNull = '\0';

	return;
}

/*
////////////////// INSTRUCTOR reverse() ///////////////
void reverse(char *s)                                                
{
   char *front, *rear, *count;
   front = s;
   count = s;

   while (*count != '\0')
   {
      count++;
   }
   rear = count - 1;
   
   while(front < rear)
   {
      char holder;
      holder = *front;
      *front = *rear;
      *rear = holder;
      front++;
      rear--;
   }
}
*/


/* Output

******
* INPUT 1 char
*****
This programs takes a C string as input, reverses characters,
then prints the result.
Enter characters from keyboard, except space or line breaks.
Press Enter when complete. >100 characters are truncated.
z

You entered:
z

Your input reversed:
z
Press any key to continue . . .

*****
* INPUT even number of characters
*****
This programs takes a C string as input, reverses characters,
then prints the result.
Enter characters from keyboard, except space or line breaks.
Press Enter when complete. >100 characters are truncated.
abcdefghijklmnopqrstuvwxyz

You entered:
abcdefghijklmnopqrstuvwxyz

Your input reversed:
zyxwvutsrqponmlkjihgfedcba
Press any key to continue . . .

*****
* INPUT odd number of characters
*****

This programs takes a C string as input, reverses characters,
then prints the result.

Enter characters from keyboard, except space or line breaks.
Press Enter when complete. >100 characters are truncated.
abcde123456

You entered:
abcde123456

Your input reversed:
654321edcba
Press any key to continue . . .



*/