ANSI/POSIX C – Page 4 – Alejandro G. Carlstein Ramos Mejia Blog

Alejandro G. Carlstein Ramos Mejia October 15, 2010 October 15, 2010 About Programming / Algorithms / ANSI/POSIX C

Example of Bubble Sort Algorithm

Example of Bubble Sort algorithm

NOTIFICATION: These examples are provided for educational purposes. Using this code is under your own responsibility and risk. The code is given ‘as is’. I do not take responsibilities of how they are used.

bubblesort.c:

/**
 * Framework for the sorting programs. 
 * Modified by: Alejandro G. Carlstein
 * Program Number: 1
 * Description: This code will implement an insertion sort algorithm
 *              which will follow the following steps:
 *              1. Copy item at current position
 *              2. Shift previous position item to current position
 *                 while item (in previous positions) is greater than
 *                 the item copied and there are previous items 
                   to compare with the key item
 *              3. Insert copied item in the previous position in which 
 *                 the previous item is found to be
 *                 smaller than the copied item
 *                 
 */
#include <stdio.h>
#define MAX_SIZE 1000000
int data[MAX_SIZE];
int n;

int main()
{
  int i;
  int j;
  int key_item;

  /* Read in the data */
  n = 0;
  while (scanf('%d', &data[n]) == 1)
    ++n;

  /* Sort the numbers low to high */
  for (i = 1; i < n; i++){

  	key_item = data[i];

  	for (j = i; (j > 0) && (data[j - 1] > key_item); j--){

 	  data[j] = data[j - 1];

 	}//end for 

 	data[j] = key_item;

  }//end for

  /* Print out the data */
  for (i = 0; i < n; ++i)
    printf('%d\n', data[i]);
}

If you encounter any problems or errors, please let me know by providing an example of the code, input, output, and an explanation. Thanks.

File Transfer Client and Server using Vigenere Cipher

[Disclaimer: This code is provided for educational purposes, you are responsible of how you use this code and this code is provided ‘as is’. Meaning that I do not take responsibility of any harm that this code may or not produce]

The following is an example of a client and server that let you transfer a file from the client to the server by encrypting and then decrypting the packages using Vigenere Cipher.

Test file content example:

Note: This program is designed only to send files that are alphabetic in lower case, without spaces, and only one line.

abcdefghijklmnopqrstuvwxyzaabcdefghijklmnopqrstuvwxyzaabcdefghijklmnopqrstuvwxyza

Makefile:

As a good policy, always add your name, short description, and any other information that could help a user that doesn’t know as you the content of your code and its behaviour.

Note: In the server, there must be a subdirectory named cli_serv in which ssh and scp can access after loading.

#########################################################################
# Author: Alejandro G. Carlstein Ramos Mejia
# Description: Client/Server File Transfer using Vergene Cipher
#
#
# make <= compile all files
# make build <= compile all files
# make all <= clean and compile all files
# make ssh <= Connect to server and go to folder cli_serv
# make upload <= Upload files on SRC_FILES list to server
# make uploadssh <= Upload files on SRC_FILES list to server and connect to server
# make submit <= Tar files on SRC_FILES list
# make zipsubmit <= Tar files on SRC_FILES list and gzip them
# make clean <= Clean all executable and *.o files
# make debug_server <= Debug server using dbg
# make debug_client <= Debug client using dbg
# make ldebug_server <= Debug for leaks on server
# make ldebug_client <= Debug for leaks on client
##########################################################################

##########################################################################
# Variables
##########################################################################

# PROJECT is the name used when preparing for sumit/
# The tar and/or zip file will be using this name
PROJECT = server_client_vergene

# SRC_FILES are list of files in the project.
# This list is used when uploading files to the server.
# Also, this list is used when tar/zipped for submit
SRC_FILES = \
	cli.c \
	serv.c\
	default.h \
	default.c \
	text.txt\
	Makefile \
	README

# OpenSSH SSH client (remote login program)
SSH = ssh

# secure copy (remote file copy program)
# SCP is used for uploading files to the server in secure mode
SCP = scp

# FOLDER_SERVER is the folder that SSH and SCP will try to access after login
FOLDER_SERVER = server_client_vergene

# SSH_SERVER is the hostname of the server
SSH_SERVER = bingsuns2.cc.binghamton.edu

# SSH_OPTION
# -t opens a pseudo-tty with in the current session.
# This flag is required to execute the commands on SSH_CD_FOLDER
SSH_OPTION = -t

# SSH_CD_FOLDER executes cd
# Then change the prompt to show the number of bash in the server
SSH_CD_FOLDER = 'cd $(FOLDER_SERVER); bash; echo $PS1'

# CC indicates which compiler is going to be used
CC = gcc

# Files required for compiling the server
CODE_SERVER_FILE = serv.c default.c

# Files required for compiling the client
CODE_CLIENT_FILE = cli.c default.c

# Name of the executable file for the server
EXEC_SERVER_FILE = serv

# Name for the executable file for the client
EXEC_CLIENT_FILE = cli

# Flags for the compiler
# -g indicate to provide debuggin information
# -Wall activates the warnings.
# -lm indicate the compiler to add basic mathematics libraries
CFLAGS = -g -Wall -lm

# COMPILE is the combination of the compiler with the flags
COMPILE = $(CC) $(CFLAGS)

# MFLAGS are flags that require to be added at the end
MFLAGS =

# USERNAME is used later when required to do an upload followed with ssh
USERNAME =

# Detect if the computer is SunOS to add flags needed for compiling
UNAME := $(shell uname)
ifeq ($(UNAME), SunOS)
 MFLAGS := -lsocket -lnsl
endif

##########################################################################
# 'make' options
##########################################################################

# Clean all files and compile client and server
all: clean compile_server compile_client

# Just build server and client
build: compile_server compile_client 

# Compile server
compile_server: $(CODE_SERVER_FILE)
	$(CC) $(CFLAGS) -o $(EXEC_SERVER_FILE) $(CODE_SERVER_FILE) $(MFLAGS)

# Compile client
compile_client: $(CODE_CLIENT_FILE)
	$(CC) $(CFLAGS) -o $(EXEC_CLIENT_FILE) $(CODE_CLIENT_FILE) $(MFLAGS)

# Debug server
debug_server:
	gdb $(EXEC_SERVER_FILE) 

# Debug client
debug_client:
	gdb $(EXEC_CLIENT_FILE) 

# Leak debug server
ldebug_server:
	valgrind --leak-check=full --show-reachable=yes -v $(EXEC_SERVER_FILE)

# Leak debug client
ldebug_client:
	valgrind --leak-check=full --show-reachable=yes -v $(EXEC_CLIENT_FILE)

# Upload files and connect to server
uploadssh:
	@echo -n 'Upload and connect to $(SSH_SERVER)- USERNAME: ';\
	read user_name;\
	$(SCP) $(SRC_FILES) $$user_name@$(SSH_SERVER):./$(FOLDER_SERVER);\
	$(SSH) $(SSH_OPTION) $$user_name@$(SSH_SERVER) $(SSH_CD_FOLDER);\

# Upload files to server
upload:
	@echo -n 'Upload to $(SSH_SERVER)- USERNAME: ';\
	read user_name;\
	$(SCP) $(SRC_FILES) $$user_name@$(SSH_SERVER):./$(FOLDER_SERVER);\

# Connect to server
ssh:
	@echo -n 'Connect to $(SSH_SERVER)- USERNAME: ';\
	read user_name;\
	$(SSH) $(SSH_OPTION) $$user_name@$(SSH_SERVER) $(SSH_CD_FOLDER);\

# Makes a archive containing all the project source files for submission.
submit:	$(SRC_FILES)
	tar -cvf $(PROJECT).tar $(SRC_FILES)

# Makes a archive containing all the project source files for submission
# and zip them
zipsubmit:	$(SRC_FILES)
	tar cvfz $(PROJECT).tar.gz $(SRC_FILES)

# Clean files
.PHONY: clean
clean:
	rm -f *~ *.o $(EXEC_SERVER_FILE) $(EXEC_CLIENT_FILE)

Default file is required for both the server and the client. It holds the libraries and definitions shared by both programs.

Default.h file:

/**
 * Author: Alejandro G. Carlstein
 * Description: File Transfer Client/Server
 */

#ifndef ACARLS_DEFAULT_H
#define ACARLS_DEFAULT_H

#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <errno.h>
#include <unistd.h>
#include <dirent.h>

/* Required for linux */
#include <string.h>

/* Required for SunOS */
#include <strings.h>

#include <ctype.h>

#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <netdb.h>

#define DEFAULT_PORT 					8414
#define DATA_PACKET_SIZE 			1024
#define NUM_BYTES							8
#define ENCRYPTION_KEY		    'security'
#define CHAR_KEY_A						97
#define CHAR_PLAIN_A					97
#define CHAR_CIPHER_A					65

#define DBG_LV0 0
#define DBG_LV1 0
#define DBG_LV2 0
#define DBG_LV3 0

#define TRUE									1
#define FALSE									0

#define QUIT_TRUE							0
#define QUIT_FALSE						1

#define CODE_FAIL							'0FAIL'
#define CODE_OK								'1OK'

#define CODE_HELLO						'100HELLO'
#define CODE_WELCOME 					'101WELCOME'
#define CODE_REQ_SERVER_NAME 	'102REQ_SERVER_NAME'

#define CODE_MSG 							'200MSG'

#define CODE_DATA							'300DATA'
#define CODE_EOF							'301EOF'
#define CODE_PUT						  '302PUT'
#define CODE_REQUEST_FILENAME	'303REQ_FILENAME'
#define CODE_REQUEST_ENCRYPT  '304REQ_ENCRYPT'
#define CODE_ENCRYPT					'305ENCRYPT'
#define CODE_REQUEST_FILE     '306REQUEST_FILE'

#define CODE_CMD							'400CMD'
#define CODE_LS								'401LS'

#define CODE_ERROR            '500ERROR'
#define CODE_ERROR_LS					'501ERROR_LS'
#define CODE_ERROR_CREAT_FILE '502ERROR_CREAT_FILE'

#define CODE_EXIT							'600EXIT'

#define MSG_ERR_WRONG_PROTOCOL  'Wrong protocol!'
#define MSG_ERROR_CREAT_FILE 		'Couldn't create file'
#define MSG_PORT_NUMBER_ONLY 		'Need port number only! \n%s <Port Number>'
#define MSG_ERR_COULDNT_SOCKET  'Couldn't obtain socket - %d'
#define MSG_ERR_COULDNT_CONNECT 'Couldn't connect!'
#define MSG_ERR_SENDING_DATA 		'Couldn't send data!'
#define MSG_ERR_RECEIVING_DATA	'Couln't recieve data!'
#define MSG_ERR_CONNECTION_FAIL 'Connection failed.'
#define MSG_ERR_NO_DIR_STREAM 	'Could not obtain the directory stream'

void debug(int debugLevel, char *fmt, ...);
void errorDoExit(char *fmt, ...);

#endif

Default.c:

/**
 * Author: Alejandro G. Carlstein
 * Description: File Transfer Client/Server
 */

#include 'default.h'

void debug(int debugLevel, char *fmt, ...){
	if (debugLevel == 1){
		va_list argp;
		fprintf(stdout, '[DBG] ');
		va_start(argp, fmt);
		vfprintf(stdout, fmt, argp);
		va_end(argp);
		fprintf(stdout, '\n');
	}
}

void errorDoExit(char *fmt, ...){
	va_list argp;
	fprintf(stderr, '[Error] ');
	va_start(argp, fmt);
	vfprintf(stderr, fmt, argp);
	va_end(argp);
	if (errno){
		fprintf(stderr, '=> %s\n', strerror(errno));
	}else{
		fprintf(stderr, '\n');
	}
	exit(1);
}

The following is the code for the server.
serv.c:

/**
 * Assignment: 1
 * Course: CS458
 * Author: Alejandro G. Carlstein
 * Description: FTP Server
 */

#include 'default.h'

/*max. length queue of pending connections may grow. */
#define MAX_BACKLOG							5
#define SETSOCKOPT_VAL  				1

#define MSG_SERVER_NAME 				'Server Name: ACARLSTEIN Server Version 1.0'
#define MSG_WAIT_CLIENT					'Waiting client...\n'
#define MSG_WAIT_CLIENT_ON_PORT	'\nTCPServer Waiting for client on port %d\n'

#define MSG_ERR_NO_SOCKET_OPT		'Couldn't set and/or get socket options'
#define MSG_ERR_UNABLE_BIND    	'Unable to bind'
#define MSG_ERR_UNABLE_LISTEN  	'Unable to Listen'
#define MSG_ERR_CANT_SEND_LIST  'Can't send server list\n'

struct Connection{
	int sock;
	int bytes_recieved;
	int port_number;
	int socket_descriptor;
	char send_data[DATA_PACKET_SIZE];
	char recv_data[DATA_PACKET_SIZE];
  struct sockaddr_in server_addr;
  struct sockaddr_in client_addr;
};

void setUpConnection(struct Connection *new_connection,
										 int port_number);
int menuDriver(struct Connection *new_connection);
void sendData(struct Connection *new_connection,
							const char* data);
int recieveData(struct Connection *new_connection);
void handShake(struct Connection* new_connection);
void sendListDirectoryContents(struct Connection* new_connection);
int receiveFileFromClient(struct Connection* new_connection);
int strdecrypt(const char* str_in,
							 char* str_out);

/**
 * MAIN
 */
int main(int argc, char *argv[]){
	debug(DBG_LV0, 'argc: %d', argc); 	

	short DO_QUIT_PROGRAM;
	int i;
	int port_number;
	socklen_t sin_size = sizeof(struct sockaddr_in);
	struct Connection connection;

	for(i = 0; DBG_LV1 && i < argc; ++i)
		debug(DBG_LV1, 'argv[%d]: %s', i, argv[i]); 		

	if (argc > 2)	errorDoExit(MSG_PORT_NUMBER_ONLY, argv[0]);

	port_number = (argc == 2) ? atoi(argv[1]) : DEFAULT_PORT;

	DO_QUIT_PROGRAM = QUIT_FALSE;
	while(DO_QUIT_PROGRAM){

		fflush(stdout);

		setUpConnection(&connection, port_number);

		printf(MSG_WAIT_CLIENT_ON_PORT, port_number);

		connection.socket_descriptor = accept(connection.sock,
													  						  (struct sockaddr *)&connection.client_addr,
																				  &sin_size);

		if (connection.socket_descriptor  == -1)
			errorDoExit(MSG_ERR_COULDNT_CONNECT);

		handShake(&connection);

 		menuDriver(&connection);

		close(connection.sock); 		

	}

  return 0;
}

/**
 * Menu driver waiting for instructions
 */
int menuDriver(struct Connection *new_connection){

	short DO_QUIT_CONNECTION;
	int bytes_received = 1;

	DO_QUIT_CONNECTION = QUIT_FALSE;
 	while (DO_QUIT_CONNECTION){  

		if(bytes_received == 0){
			DO_QUIT_CONNECTION = QUIT_TRUE;
		}else{

			printf(MSG_WAIT_CLIENT);

			bytes_received = recieveData(new_connection);
			if (strcmp(new_connection->recv_data, CODE_LS) == 0){
				sendListDirectoryContents(new_connection);
			}else
			if (strcmp(new_connection->recv_data, CODE_PUT) == 0){
				bytes_received = receiveFileFromClient(new_connection);
			}else{
				close(new_connection->sock);
				fprintf(stderr, MSG_ERR_WRONG_PROTOCOL ' - PUT\n');
				DO_QUIT_CONNECTION = QUIT_TRUE;
			}
		}
	}
	return 0;
}

/**
 * Set up connection with the client
 */
void setUpConnection(struct Connection *new_connection,
										 int port_number){
	debug(DBG_LV0, 'setUpConnection(port_number: %d)', port_number);

	int opt_val = SETSOCKOPT_VAL;
	new_connection->port_number = port_number;

  if ((new_connection->sock = socket(AF_INET, SOCK_STREAM, 0)) == -1)
		errorDoExit(MSG_ERR_COULDNT_SOCKET, new_connection->sock);

	if (setsockopt(new_connection->sock, SOL_SOCKET, SO_REUSEADDR, &opt_val, sizeof(int)) == -1)
		errorDoExit(MSG_ERR_NO_SOCKET_OPT);

	debug(DBG_LV1, 'Got socket!');

  new_connection->server_addr.sin_family = AF_INET;
 	debug(DBG_LV1,'sin_family');      

  new_connection->server_addr.sin_port = htons(port_number);
	debug(DBG_LV1,'sin_port');

  new_connection->server_addr.sin_addr.s_addr = INADDR_ANY;
	debug(DBG_LV1, 'sin_addr');

  bzero(&(new_connection->server_addr.sin_zero), NUM_BYTES);
	debug(DBG_LV1,'sin_zero');

	// bind a name to a socket
  if (bind(new_connection->sock,
  				(struct sockaddr *)&new_connection->server_addr,
  				sizeof(struct sockaddr)) == -1){
		close(new_connection->sock);
		errorDoExit(MSG_ERR_UNABLE_BIND);
	}

	// Listen for connection on the socket
  if (listen(new_connection->sock, MAX_BACKLOG) == -1){
		close(new_connection->sock);
   	errorDoExit(MSG_ERR_UNABLE_LISTEN);
  }
	debug(DBG_LV1, 'Listening...');	

}

/**
 * Send data to client
 */
void sendData(struct Connection *new_connection,
							const char* data){
	debug(DBG_LV0, 'sendData(data: %s)', data);

 	int data_length;

	bzero(new_connection->send_data, DATA_PACKET_SIZE);
 	strcpy(new_connection->send_data, data);
 	data_length = strlen(new_connection->send_data);

 	debug(DBG_LV1, 'new_connection->send_data: %s',
 	      new_connection->send_data);

	if (send(new_connection->socket_descriptor,
					 new_connection->send_data,
					 data_length, 0) != data_length){
		close(new_connection->sock);
		fprintf(stderr, MSG_ERR_SENDING_DATA '\n');
	}
}

/**
 * Receive data from client
 */
int recieveData(struct Connection *new_connection){
	debug(DBG_LV0, 'recieveData()');

	bzero(new_connection->recv_data, DATA_PACKET_SIZE);
	int bytes_recieved = recv(new_connection->socket_descriptor,
														new_connection->recv_data,
														DATA_PACKET_SIZE,
														0);		

	debug(DBG_LV1, 'Check bytes received');

	if(bytes_recieved < 1){

		close(new_connection->sock);

		if(bytes_recieved == 0){
			fprintf(stderr, MSG_ERR_CONNECTION_FAIL '\n');
		}else{
			fprintf(stderr,MSG_ERR_RECEIVING_DATA '\n');
		}

	}else{

		debug(DBG_LV1, 'Received: %s', new_connection->recv_data);

		new_connection->bytes_recieved = bytes_recieved;
  	new_connection->recv_data[bytes_recieved] = '\0';
  }

  return bytes_recieved;
}

/**
 * Hand shake with client to test own protocol
 */
void handShake(struct Connection* new_connection){
	debug(DBG_LV0, 'handShake()');

	printf('Connection from (%s , %d)...\n',
         inet_ntoa(new_connection->client_addr.sin_addr),
         ntohs(new_connection->client_addr.sin_port));

	debug(DBG_LV1,' If client say HELLO, Greed client with WELCOME');
 	recieveData(new_connection);
	if (strcmp(new_connection->recv_data, CODE_HELLO) == 0){
		debug(DBG_LV1, 'Client handshake with server');
		sendData(new_connection, CODE_WELCOME);
	}else{
		close(new_connection->sock);
		fprintf(stderr, MSG_ERR_WRONG_PROTOCOL ' - HELLO/WELCOME \n');
	}

	debug(DBG_LV0,'If client ask for server name send server name to client');
 	recieveData(new_connection);
	if (strcmp(new_connection->recv_data, CODE_REQ_SERVER_NAME) == 0){
		debug(DBG_LV1, 'Client asking for server name');
		sendData(new_connection, MSG_SERVER_NAME);
	}else{
		close(new_connection->sock);
		fprintf(stderr, MSG_ERR_WRONG_PROTOCOL ' - SERVER NAME\n');
	}
}

/**
 * Send list of directory contents to client
 */
void sendListDirectoryContents(struct Connection* new_connection){
	debug(DBG_LV0, 'void displayLocalListDirectoryContents()');
	int bytes_received;
	struct dirent *dirent_struct_ptr;
	DIR *directory_stream_ptr;

	if ((directory_stream_ptr = opendir('./')) != NULL){

  	while ((dirent_struct_ptr = readdir(directory_stream_ptr))){
			sendData(new_connection, dirent_struct_ptr->d_name);				

			bytes_received = recieveData(new_connection);
			if (strcmp(new_connection->recv_data, CODE_OK) != 0){
				fprintf(stderr, MSG_ERR_CANT_SEND_LIST);
			}
   	}
		sendData(new_connection, CODE_EOF);			  		

	}else{
		sendData(new_connection, CODE_ERROR_LS);
		errorDoExit(MSG_ERR_NO_DIR_STREAM);
	}

}

/**
 * Receive encrypted file from client
 */
int receiveFileFromClient(struct Connection* new_connection){
	debug(DBG_LV0, 'void receiveFileFromClient(is_encrypted: %s)');											

	int bytes_received;

	char filename[DATA_PACKET_SIZE];
	char filename_se[DATA_PACKET_SIZE];
	char filename_sd[DATA_PACKET_SIZE];
	char str_unencrypted[DATA_PACKET_SIZE];
	FILE *fp_se, *fp_sd;

	/* Request filename */
	debug(DBG_LV1, 'Request filename from client');
	sendData(new_connection, CODE_REQUEST_FILENAME);

	/* receive filename */
	bytes_received = recieveData(new_connection);
	strcpy(filename, new_connection->recv_data);
	sprintf(filename_se, '%s_se', filename);
	sprintf(filename_sd, '%s_sd', filename);

	debug(DBG_LV1, 'filename: %s', filename);
	debug(DBG_LV1, 'filename_se: %s', filename_se);
	debug(DBG_LV1, 'filename_sd: %s', filename_sd);	

	fp_se = fopen(filename_se, 'w');
	fp_sd = fopen(filename_sd, 'w');
	debug(DBG_LV1, 'Files open');

	if (fp_se == NULL || fp_sd == NULL){
		debug(DBG_LV1, 'Error, closing files');
		fclose(fp_se);
		fclose(fp_sd);
		errorDoExit(MSG_ERROR_CREAT_FILE);
	}else{

		debug(DBG_LV1, 'Download file...');
		/* Send code request file */
		sendData(new_connection, CODE_REQUEST_FILE);				

		bytes_received = recieveData(new_connection);

  	/* while loop until eof */
  	while (strcmp(new_connection->recv_data, CODE_EOF) != 0){

			debug(DBG_LV1, 'Saving: %s', new_connection->recv_data);
	  	/* save encrypted package */
			fprintf(fp_se, '%s', new_connection->recv_data);

			/* Decencrypt package */
			bzero(str_unencrypted, DATA_PACKET_SIZE);
			strdecrypt(new_connection->recv_data, str_unencrypted);
			debug(DBG_LV1, 'Decrypt: %s\n', new_connection->recv_data);

			/* Save unecrypted package */
			debug(DBG_LV1, 'DECRYPT: %s', str_unencrypted);

			fprintf(fp_sd, '%s', str_unencrypted);

			debug(DBG_LV1, 'Sending OK...');
	  	/*send ok */
			sendData(new_connection, CODE_OK);
			bytes_received = recieveData(new_connection);
  	}

	}	

	fclose(fp_se);
	fclose(fp_sd);
	return 0;
}

/**
 * Decrypt string
 */
int strdecrypt(const char* str_in,
							 char* str_out){
	debug(DBG_LV0, 'strdencrypt(str_in: %s)', str_in);

	int i, j;
	int i_cipher, i_key, i_temp;
	char str_key[DATA_PACKET_SIZE];
	strcpy(str_key, ENCRYPTION_KEY);
	char char_temp;
	for (i = 0, j = 0; i < strlen(str_in); ++i, ++j){

		i_cipher = str_in[i] - CHAR_CIPHER_A;
		i_key = str_key[j] - CHAR_KEY_A;
		i_temp = i_cipher - i_key;

		debug(DBG_LV1, 'Ci([%c]%d): %d, Ki([%c]%d): %d, Ci - Ki: %d',
					str_in[i], i, i_cipher, str_key[j], j, i_key, i_temp);

		if (i_temp > -1){
			//COMMON KNOWN DECRYPT ALGORIGHTM
			i_temp = ((i_temp) % 26);
		}else{
			//DECRYPT ALGORITHM FOR UNCOMMON CASES WHERE I_TEMP IS NEGATIVE
			i_temp = ((i_temp + 26) % 26);
		}

		char_temp = i_temp + CHAR_PLAIN_A;
		if (isalpha(char_temp)){
			str_out[i] = char_temp;
		}else{
			str_out[i] = '\0';
		}

		if ( (j + 1) >= strlen(str_key)) j = -1;
	}

	return 0;
}

The following is the code for the client.

cli.c

/**
 * Assignment: 1
 * Course: CS458
 * Author: Alejandro G. Carlstein
 * Description: Transfer Encrypted File Client
 */

#include 'default.h'

#define DEFAULT_HOST 									'localhost'
#define EXIT_PROGRAM 									0
#define DONT_EXIT_PROGRAM 						1

#define CMD_QUIT											'quit'
#define CMD_HELP											'help'
#define CMD_LS												'ls'
#define CMD_LLS												'lls'
#define CMD_LPWD											'lpwd'
#define CMD_PUT												'put'

#define MSG_DISPLAY_MENU 							'User help:\n'\
																			'help - Display help option\n'\
																		  'lls  - Display local directory list contents\n'\
                    				          'lpwd - Display local current directory\n'\
                    				          'put  - Transfer local file to server\n'\
                    				          '  put <file to transfer>\n'\
                    				          'quit - Quit program\n'

#define MSG_ERROR_UNKNOWN_COMMAND			'[X] Command not recognized: %s\n'
#define MSG_ERROR_GETTING_HOSTNAME 		'Couln't get hostname!'
#define MSG_ERROR_SERVER_DISCONNECTED 'Server disconnected...\n'

enum TOKENS{
	TOKEN_COMMAND,
	TOKEN_FILENAME,
	MAX_TOKENS
};

struct Connection{
	int sock;
	int bytes_received;
	int port_number;
	char send_data[DATA_PACKET_SIZE];
	char recv_data[DATA_PACKET_SIZE];
	struct hostent *host;
  struct sockaddr_in server_addr;
};

void getConnection(struct Connection *new_connection,
									 char *hostname,
									 int port_number);
void menuDriver(struct Connection *new_connection);
int receiveData(struct Connection *new_connection);
int sendData(struct Connection* new_connection, const char* data);
void handShake(struct Connection* new_connection);
void promptUser(char* tokens[]);
void displayHelp(void);
void displayLocalListDirectoryContents(void);
void printNameCurrentDirectory(void);
void receiveListDirectoryContents(struct Connection *new_connection);
void putFileOnServer(struct Connection *new_connection,
										 const char* filename);
int strencrypt(const char* str_in,
               char* str_out);
/**
 * MAIN
 */
int main(int argc, char* argv[]){
	debug(DBG_LV0, 'argc: %d', argc); 	

	int i;
	int port_number = (argc >= 3 ) ? atoi(argv[2]) : DEFAULT_PORT;
	char* host_name = (argc >= 2) ? argv[1] : DEFAULT_HOST;

	struct Connection connection;

	for(i = 0; i < argc; ++i)
		debug(DBG_LV0, 'argv[%d]: %s', i, argv[i]); 		

	if (argc > 3)
		errorDoExit(MSG_PORT_NUMBER_ONLY, argv[0]);

	debug(DBG_LV1, 'host: %s', host_name);

	getConnection(&connection, host_name, port_number);

	handShake(&connection);

	menuDriver(&connection);

	return 0;

}

/**
 * Driver menu
 */
void menuDriver(struct Connection *new_connection){
	debug(DBG_LV0, 'menuDriver()');

	short doExit = DONT_EXIT_PROGRAM;
	int i;
	char* tokens[MAX_TOKENS] = {NULL, NULL};
	char command[DATA_PACKET_SIZE];
	char filename[DATA_PACKET_SIZE];

  while(doExit){

		promptUser(tokens);				

		for (i = 0; DBG_LV1 && i < MAX_TOKENS; ++i)
			debug(DBG_LV1, 'TOKEN[%d]: %s', i, tokens[i]);

		/* Must copy string to work on SunOS */
		if (tokens[TOKEN_COMMAND] != NULL){
			strcpy(command, tokens[TOKEN_COMMAND]);
   		debug(DBG_LV1, '[Command: %s]', command);
		}

		if (tokens[TOKEN_FILENAME] != NULL){
    	strcpy(filename, tokens[TOKEN_FILENAME]);
	    debug(DBG_LV1, '[Filename: %s]', filename);
    }

		/* MENU */

		if (strcmp(command, CMD_QUIT) == 0){
			debug(DBG_LV1, 'COMMAND> %s: ', CMD_QUIT);
			close(new_connection->sock);
			printf('Bye Bye\n');
			doExit = EXIT_PROGRAM;

		}else
		if (strcmp(command, 'help') == 0){
			debug(DBG_LV1, 'COMMAND> %s ', CMD_HELP);
			displayHelp();

		}else
		if (strcmp(command, CMD_LLS) == 0){
			debug(DBG_LV1, 'COMMAND> %s ', CMD_LLS);
			displayLocalListDirectoryContents();

		}else
		if (strcmp(command, CMD_LLS) == 0){
			debug(DBG_LV1, 'COMMAND> %s ', CMD_LLS);
			displayLocalListDirectoryContents();

		}else
		if (strcmp(command, CMD_LS) == 0){
			debug(DBG_LV1, 'COMMAND> %s ', CMD_LS);
			receiveListDirectoryContents(new_connection);

		}else
		if (strcmp(command, CMD_LPWD) == 0){
			debug(DBG_LV1, 'COMMAND> %s ', CMD_LPWD);
			printNameCurrentDirectory();

		}else
		if (strcmp(command, CMD_PUT) == 0){
			debug(DBG_LV1, 'COMMAND> %s ', CMD_PUT);
			putFileOnServer(new_connection, filename);

		}else{
			printf(MSG_ERROR_UNKNOWN_COMMAND, command);
		}

	}

}

/**
 * Obtain connection with server
 */
void getConnection(struct Connection *new_connection,
									 char *hostname,
									 int port_number){
	debug(DBG_LV0, 'getConnection(hostname: %s, port_number: %d)', hostname, port_number);

	if ((new_connection->host = gethostbyname(hostname)) == NULL)
		errorDoExit(MSG_ERROR_GETTING_HOSTNAME);

	new_connection->port_number = port_number;	

	if ((new_connection->sock = socket(AF_INET, SOCK_STREAM, 0)) == -1)
		errorDoExit(MSG_ERR_COULDNT_SOCKET, new_connection->sock);

	debug(DBG_LV1, 'Got socket!');

  new_connection->server_addr.sin_family = AF_INET;
	debug(DBG_LV1,'sin_family');

  new_connection->server_addr.sin_port = htons(port_number);
	debug(DBG_LV1,'sin_port');

  new_connection->server_addr.sin_addr = *((struct in_addr *)new_connection->host->h_addr);
	debug(DBG_LV1, 'sin_addr');

	// bzero() is used only for setting the values to zero
	bzero(&(new_connection->server_addr.sin_zero), NUM_BYTES);
	debug(DBG_LV1,'sin_zero');

  if (connect(new_connection->sock,
  					  (struct sockaddr *)&new_connection->server_addr,
  					  sizeof(struct sockaddr)) == -1)
		errorDoExit(MSG_ERR_COULDNT_CONNECT);

	debug(DBG_LV1, 'Got connection!');
}

/**
 * Receive data
 * @Return: Number of bytes received
 */
int receiveData(struct Connection *new_connection){
	debug(DBG_LV0, 'receiveData()');

	bzero(new_connection->recv_data, DATA_PACKET_SIZE);
	int bytes_received = recv(new_connection->sock,
														new_connection->recv_data,
														DATA_PACKET_SIZE,
														0);		

	if(bytes_received < 1){
		close(new_connection->sock);
		if(bytes_received == 0){
			close(new_connection->sock);
			printf(MSG_ERROR_SERVER_DISCONNECTED);
			errorDoExit(MSG_ERR_CONNECTION_FAIL);		

		}else{
			errorDoExit(MSG_ERR_RECEIVING_DATA);
		}
	}

	debug(DBG_LV1, 'Received (%d): %s',
				strlen(new_connection->recv_data), new_connection->recv_data);	

	new_connection->bytes_received = bytes_received;
  new_connection->recv_data[bytes_received] = '\0'; 

  return bytes_received;
}

/**
 * Send data
 * @Return: Number of bytes sended
 */
int sendData(struct Connection* new_connection,
						const char* data){
	debug(DBG_LV0, 'sendData(%s)', data);
	int data_length;

	bzero(new_connection->send_data, DATA_PACKET_SIZE);
	strcpy(new_connection->send_data, data);
	data_length = strlen(new_connection->send_data);

	if (send(new_connection->sock, new_connection->send_data,
					 data_length, 0) != data_length){
		close(new_connection->sock);
		errorDoExit(MSG_ERR_SENDING_DATA);
	}

	return data_length;
}

/**
 * Hand shake with the server to verify own protocol
 */
void handShake(struct Connection* new_connection){
	debug(DBG_LV0, 'handShake()');

	debug(DBG_LV1, 'Sending HELLO message...');
	sendData(new_connection, CODE_HELLO);

	debug(DBG_LV1, 'Getting WELCOME message...');
	receiveData(new_connection);  		

	if (strcmp(new_connection->recv_data, CODE_WELCOME) > -1){
		debug(DBG_LV1, 'Got WELCOME!');

		debug(DBG_LV1, 'Request server name');
		sendData(new_connection, CODE_REQ_SERVER_NAME);

		receiveData(new_connection);
		printf('Server Name: %s\n', new_connection->recv_data);
	}else{
		errorDoExit(MSG_ERR_WRONG_PROTOCOL);
	}
}

/**
 * Prompt user for input
 */
void promptUser(char* tokens[]){
	char str_input[DATA_PACKET_SIZE];
	char *p;
	int i;

	printf('\nftp> ');
	fgets(str_input, DATA_PACKET_SIZE, stdin);		

	p = strtok(str_input, ' \n');
  for (i = 0; p != NULL; (p = strtok(NULL, ' \n')), i++)
		tokens[i] = p;
}

/**
 * Display help message
 */
void displayHelp(void){
	debug(DBG_LV0, 'displayHelp()');
	printf(MSG_DISPLAY_MENU);
}

/**
 * Display local list directory contents
 */
void displayLocalListDirectoryContents(void){
	debug(DBG_LV0, 'void displayLocalListDirectoryContents()');

	struct dirent *dirent_struct_ptr;
	DIR *directory_stream_ptr;

	if ((directory_stream_ptr = opendir('./')) != NULL){
		printNameCurrentDirectory();

  	while ((dirent_struct_ptr = readdir(directory_stream_ptr))){
	  	printf(' %s\n',dirent_struct_ptr->d_name);
   	}
	}else{
		errorDoExit(MSG_ERR_NO_DIR_STREAM);
	}

}

/**
 * Print the name of the current directory
 */
void printNameCurrentDirectory(void){
	debug(DBG_LV0, 'void printNameCurrentDirectory()');

	long size;
	char *buf;
	char *ptr;
	size = pathconf('.', _PC_PATH_MAX);
	if ((buf = (char *)malloc((size_t)size)) != NULL){
		ptr = getcwd(buf, (size_t)size);
	}else{
		errorDoExit('Could not obtain the current directory');
	}
	printf('Current Directory: %s\n', ptr);
}

/**
 * Receive the list of directory contents from the server
 */
void receiveListDirectoryContents(struct Connection *new_connection){
	debug(DBG_LV0, 'receiveListDirectoryContents()');

	sendData(new_connection, CODE_LS);

	receiveData(new_connection);
	while (strcmp(new_connection->recv_data, CODE_EOF) != 0){

		if (strcmp(new_connection->recv_data, CODE_ERROR_LS) == 0){
			fprintf(stderr, 'Couldn't read list directory contents!\n');
			break;
		}else{
			printf('%s\n', new_connection->recv_data);
			sendData(new_connection, CODE_OK);
		}
		receiveData(new_connection);
	}

}

/**
 * Put an encrypted file on the server
 */
void putFileOnServer(struct Connection *new_connection,
										 const char* filename){
	debug(DBG_LV0, 'void putFileOnServer(filename: %s)', filename);

	char str_filename[DATA_PACKET_SIZE];
	char filename_ce[DATA_PACKET_SIZE];
	char str_in_file[DATA_PACKET_SIZE];
	char str_in_file_encrypt[DATA_PACKET_SIZE];
	FILE *fp, *fp_ce;

	strcpy(str_filename, filename);

	debug(DBG_LV1, 'str_filename: %s', str_filename);

	sprintf(filename_ce, '%s_ce', str_filename);

	debug(DBG_LV1, 'filename_ce: %s', filename_ce);

	debug(DBG_LV1, 'OPEN FILE TO READ');
	fp = fopen(str_filename, 'r');

	debug(DBG_LV1, 'OPEN FILE TO WRITE');
	fp_ce = fopen(filename_ce, 'w');

	if (fp == NULL || fp_ce == NULL){
		fclose(fp_ce);
		fclose(fp);
		errorDoExit('Couldn't open file');
	}else{

		/* Send PUT code to server */
		sendData(new_connection, CODE_PUT);

		debug(DBG_LV0, 'Waiting for CODE_REQUEST_FILENAME');
		/* Receive filename request form server */
		receiveData(new_connection);
		if (strcmp(new_connection->recv_data, CODE_REQUEST_FILENAME) == 0){

			debug(DBG_LV0, 'Send filename');
			/* Send filename to server */
			sendData(new_connection, str_filename);

			/* Receive request to send file */
			receiveData(new_connection);
			if (strcmp(new_connection->recv_data, CODE_REQUEST_FILE) == 0){
				printf('Sending file: %s.\n', filename);
					/* Encrypt file */
				while(fgets(str_in_file, DATA_PACKET_SIZE, fp) != NULL){
					debug(DBG_LV2, 'Reading (Len: %d): %s', strlen(str_in_file), str_in_file);						

					/* encrypt package */
					strencrypt(str_in_file, str_in_file_encrypt);

					/* Save it in <filename>_ce */
					fprintf(fp_ce, '%s', str_in_file_encrypt);					

					/* send packages */
					sendData(new_connection, str_in_file_encrypt);

					/* Waiting for ok */
					receiveData(new_connection);
					if (strcmp(new_connection->recv_data, CODE_OK) == 0){
						printf('OK');
					}else{
						errorDoExit('Wrong protocol - Waiting OK');
					}	

				}
				sendData(new_connection, CODE_EOF);			

			}else{
				errorDoExit('Wrong protocol - Waiting request for file ');
			}

		}else{
			errorDoExit('Wrong protocol - Waiting for request of filename');
		}

	}

	fclose(fp);
	fclose(fp_ce);

}

/**
 * Encrypt the string using key
 * @Return: Number of bytes encrypted
 */
int strencrypt(const char* str_in,
               char* str_out){
	debug(DBG_LV0, 'strencrypt(str_in: %s)', str_in);

	int i, j;
	int i_plain, i_key;

	char str_key[DATA_PACKET_SIZE];

	strcpy(str_key, ENCRYPTION_KEY);

	for (i = 0, j = 0; i < strlen(str_in) - 1; ++i, ++j){

		i_plain = (unsigned int)str_in[i] - CHAR_PLAIN_A;
		i_key = (unsigned int)str_key[j] - CHAR_KEY_A;

		str_out[i] = (char)((i_plain + i_key) % 26 + CHAR_CIPHER_A);

		debug(DBG_LV1, '(str_out: %d) [%c:%d] = (str_in:%d)[%c:%d], (key:%d)[%c:%d]',
					i, str_out[i], (int)str_out[i],
					i, str_in[i], (int) str_in[i],
					j, str_key[j], (int)str_key[j]);

		if ( (j + 1) >= strlen(str_key)) j = -1;
	}

	return strlen(str_in);
}

When I wrote the code, I was following certain guidelines. As you may think the code could be written better. I agree.

In case you have any questions about the code please post them. I will try to answer you as soon as possible.

Algorithms Examples in ANSI C

Here are some examples of Algorithm written in ANSI C.
Even do they are written in ANSI C, I would advice to compile them in Linux as I did. If you encounter any problems or errors, please let me know by providing an example of the code, input, output, and an explanation. Thanks.
NOTIFICATION: These examples are provided for educational purposes. Using this code is under your own responsibility and risk. I do not take responsibilities of how they are used.

Bubble sort. Code
Example code: carlstein_p01.c – Test File: carlstein_p01_integers.txt
Heap sort
Example code: carlstein_p02.c – Test File: carlstein_p02_integers_1.txt
Binary Search using Heapsort
Example code: carlstein_p03.c – Test Files: carlstein_p03_integers _1.txt, carlstein_p03_integers_2.txt
Quicksort using Hoarse partition and random partition
Example code: carlstein_p04.c – Test Files: carlstein_p04_integers_1.txt, carlstein_p04_integers_2.txt
Knapsack
Example code: carlstein_p05.c – Test Files: carlstein_p05_integer_1.txt, carlstein_p05_integer_2.txt, carlstein_p05_integers_3.txt
Ferry Loading
Example code: carlstein_p06.c – Test Files: carlstein_p06_input_1.txt, carlstein_p06_input_2.txt, carlstein_p06_input_3.txt, carlstein_p06_input_4.txt
Huffman algorithm using heap
Example code: carlstein_p07.c – Test Files: carlstein_p07_input_1.txt, carlstein_p07_input_2.txt, carlstein_p07_input_3.txt, carlstein_p07_input_4.txt
Kurskay’s algorithm using Disjoint Sets and heap
Example code: carlstein_p08.c – Test Files: carlstein_p08_input_1.txt, carlstein_p08_input_2.txt, carlstein_p08_input_3.txt, carlstein_p08_input_4.txt
Disjktra algorithm using heap
Example code: carlstein_p09.c – Test Files: carlstein_p09_input_1.txt, carlstein_p09_input_2.txt, carlstein_p09_input_3.txt, carlstein_p09_input_4.txt
Vertex Cover algorithm using heap
Example code: carlstein_p10.c – Test Files: carlstein_p10_input_1.txt, carlstein_p10_input_2.txt, carlstein_p10_input_3.txt, carlstein_p10_input_4.txt, carlstein_p10_input_5.txt, carlstein_p10_input_6.txt, carlstein_p10_input_7.txt