/* Filename: HW6.c */
/* This program encodes and decodes messages*/


/******************************************************************
 *                                                                *
 * Programmer: Matthew Glynn                                      *
 * Date : 03/08/2007                                              *
 * Section Number: B36                                            * 
 * Filename: HW6.c                                                *
 * Description: This program encodes and decodes messages         *
 *                                                                *
 ******************************************************************/



#include <stdio.h> /* library to be used */


/* Declare functions */
	void printMenu( void );
	void encode( void );
	void decode( void );



/* Declare Global variables */

	char alphabet[26] = {'a'/*1*/, 'b'/*2*/, 'c'/*3*/, 'd'/*4*/, 'e'/*5*/, 'f'/*6*/, 'g'/*7*/, 'h'/*8*/, 'i'/*9*/, 'j'/*10*/, 'k'/*11*/, 'l'/*12*/, 'm'/*13*/, 'n'/*14*/, 'o'/*15*/, 'p'/*16*/, 'q'/*17*/, 'r'/*18*/, 's'/*19*/, 't'/*20*/, 'u'/*21*/, 'v'/*22*/, 'w'/*23*/, 'x'/*24*/, 'y'/*25*/, 'z'/*26*/} ;          

  	char cipher[26] =   {'m'/*1*/, 'a'/*2*/, 't'/*3*/, 'h'/*4*/, 'e'/*5*/, 'w'/*6*/, 'g'/*7*/, 'l'/*8*/, 'y'/*9*/, 'n'/*10*/, 'r'/*11*/, 'f'/*12*/, 's'/*13*/, 'd'/*14*/, 'k'/*15*/, 'i'/*16*/, 'j'/*17*/, 'u'/*18*/, 'v'/*19*/, 'p'/*20*/, 'x'/*21*/, 'q'/*22*/, 'z'/*23*/, 'o'/*24*/, 'b'/*25*/, 'c'/*26*/} ;

	char message[500];		

	char junk;/* for the /n */


	int counter, counter2, length, choice;

	char *alphabetPtr = alphabet;
	char *cipherPtr = cipher;
	char *messagePtr = message;
		


int main( void )

{/* start main */

			 

	do 

		{/* start do */
		
			printMenu();/* CALL FUNCTION PRINTMENU*/

			
			switch ( choice )/* Switch on menu choice entered by user */
								{
									
									case 1:

										encode();/* CALL FUNCTION encode*/
							
										break;
									
									case 2:

										decode();/* CALL FUNCTION decode*/

										break;
								
									case 3:


										break;

									default:  /* display default when a choice <0 or >4 has been entered */
										
										printf("  An invalid entry was made.\n");
										
										break;
								}

		}
			while (choice !=3); /* when an entry of 3 is made, exit program */

		return 0; /* indicate program ended successfully */

}/* End funcyion main */


/******************************************************************
 *                                                                *
 * Programmer: Matthew Glynn                                      *
 * Name: printMenu                                                *
 * Function: This function prints the main menu of the program.   *
 * Algorithm: This function is a series of printf statements.     *
 * Input: none                                                    *
 * Output: changes the global variable choice, so no real output  *
 *                                                                *
 ******************************************************************/
void printMenu( void )
{
		 
		printf("\n 1. Encode a message\n");
		printf(" 2. Decode a message\n");
		printf(" 3. Exit the program\n");
		scanf("%d", &choice);

		printf("\n");
	
}


/******************************************************************
 *                                                                *
 * Programmer: Matthew Glynn                                      *
 * Name: encode                                                   *
 * Function: Encodes the message using arrays                     *
 * Input: Global Variables                                        *
 *                                                                *
 * Output: displayes global variable so no real output            *
 ******************************************************************/
void encode( void )
{
	
		printf("Enter message to encode:");
		scanf("%c", &junk);
		fgets(message, 500, stdin);
		length=(strlen(message));
		for (counter=0; counter < length; counter = counter + 1)
		{
			int found = 0;
			for (counter2=0; counter2<=25; counter2 = counter2 + 1)
			{
				if (message[counter]==alphabet[counter2])
				{
					printf("%c", cipher[counter2]);
					found = 1;
				}
			}
				if (!found)
				printf("%c", message[counter]);
		}


}

/******************************************************************
 *                                                                *
 * Programmer: Matthew Glynn                                      *
 * Name: decode                                                   *
 * Function: Decodes message using pointer arithmetic             *
 * Input: Global Variables                                        *
 *                                                                *
 * Output: displayes global variable so no real output            *
 ******************************************************************/
void decode( void )
{
		printf("Enter message to decode:");
		scanf("%c", &junk);
		fgets(message, 500, stdin);
		length=(strlen(message));
		for (counter=0; counter < length; counter = counter + 1)
		{
			int found = 0;
			for (counter2=0; counter2<=25; counter2 = counter2 + 1)
			{
				if (*(messagePtr+counter)==*(cipherPtr+counter2))
				{
					printf("%c", *(alphabetPtr+counter2));
					found = 1;
				}
			}
				if (!found)
				printf("%c", *(messagePtr+counter));
			
		}

}