Linked List of Linked list of linked list : problem with a condtion

This is a discussion on Linked List of Linked list of linked list : problem with a condtion within the C Programming forums, part of the General Programming Boards category; Hi ! This is a program which creates 3D linked list Linked list of airlines, Each struct holds a node ...

  1. #1
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    Linked List of Linked list of linked list : problem with a condtion

    Hi !

    This is a program which creates 3D linked list
    Linked list of airlines, Each struct holds a node to a list of flights for that airline and and each airline holds a node to a list of passengers for that flight.

    Here is some quick background about the program There is a function for each list which creates a node for that list and places it in the alphabetical order in that list.

    a)airline* create_airline_node(airline *start1) : creates airline node
    b)flight* create_flight_node(flight *start2) : creates flight node
    c)passenger* create_passenger_node(passenger *start3): creates passenger node

    each node has a for loop which traversers through the list and compares the name entered enteres it at the right position alphabetically.

    Now here are my PROBLEMS:

    1. the condition tested in the for loops in the functions given above looks like this

    (count_node1 != NULL) && (strcmp(count_node1->airlinename, node->airlinename) <= 0)

    If i change this condtion to :

    (strcmp(count_node1->airlinename, node->airlinename) <= 0) &&
    (count_node1 != NULL)

    the function doesn't work properly it gives me an error if the second name entered is greater that the first ????????????

    any explantion would be a great help

    2. I need an idea to iplement this program in files..????

    Here is the code:

    Code:
    #include<stdio.h>
    #include<stdlib.h>
    #include<string.h>
    
     
    struct flight;                               //Forward Declarations of Flight structure
    
    
    //-----------------------------------   AIRLINE LIST STRUCTURE AND FUNCTION DECLARATIONS ----------------------------------------
    
    
    
    struct airline                          // Structure for Airline node, includes strings for Airline name 
    {                                      // pointer locations to the next airline and also to the flight list for that airline         
    	char *airlinename;
    	struct airline *next;
    	struct flight *node1;
    } *start1 = NULL;
    
    
    airline* create_airline_node(airline *start1);             //Function Declarations
    airline* enter_airline_info(airline *node);
    airline* delete_airline_node(airline *start1);
    void print_airline_list(airline *start1);
    airline* enter_flight_menu(airline *start1);
    airline* airline_menu(airline *start1);
    
    
    
    
    //-----------------------------------   FLIGHT LIST STRUCTURE AND FUNCTION DECLARATIONS ----------------------------------------
    
    struct passenger;                              //Forward Declarations of passenger structure
    
    
    struct flight                          // Structure for flight node, includes strings for flightname, from, to and time with 
    {                                      // pointer locations to the next flight and also to the passenger list          
    	char *flightname;
    	char *departure_location;
    	char *arrival_location;
    	char *take_off_time;
    	struct flight *next;
    	struct passenger *node2;
    } *start2 = NULL;
    
    
    flight* create_flight_node(flight *start2);             //Function Declarations
    flight* enter_flight_info(flight *node);
    flight* delete_flight_node(flight *start2);
    void print_flight_list(flight *start2);
    flight* enter_passenger_menu(flight *start2);
    flight* flight_menu(flight *start2);
    
    
    
    //-----------------------------------   PASSENGER LIST STRUCTURE AND FUNCTION DECLARATIONS ----------------------------------------
    
    
    struct passenger                                 //Passenger Structure includes name of the passenger and the ponter to the next
    {                                                // passenger node, structure declaration also declares start as the first node
    	char *name;                                  // and declares it NULL.
    	struct passenger *next;
    } *start3 = NULL;
    
    
    
    passenger* create_passenger_node(passenger *start3);             //Function Declarations
    passenger* enter_passenger_info(passenger *node);
    passenger* delete_passenger_node(passenger *start3);
    passenger* passenger_menu(passenger *start3);
    void print_passenger_list(passenger *node); 
    
    
    
    
    //----------------------------- MEMBER FUNCTIONS TO MANIPULATE THE AIRLINE LINKED LIST --------------------------------------------
    
    
    airline* create_airline_node(airline *start1)         // Creates a sorted list of airlines (default entry sort condition by airline name)
    {                                                   // by entering the airline name in a node at the sorted position, 
                                                        // it calls the function "enter_airline_info() to ask the 
    	if (start1 == NULL)                             // user for its information
    	{
    		start1 = (airline *) malloc(sizeof(airline));
    		start1 = enter_airline_info(start1);
    		start1->next = NULL;
    	}
    	else
    	{
    		airline *count_node1, *count_node2, *node;
    		node = (airline *) malloc(sizeof(airline));
    		node = enter_airline_info(node);
    		for (count_node1 = start1; (count_node1 != NULL) && (strcmp(count_node1->airlinename, node->airlinename) <= 0); count_node2 = count_node1, count_node1 = count_node1->next);
    		if(count_node1 == start1)
    		{
    			node->next = start1;
    			start1 = node;
    		}
    		else if (count_node1 == NULL)
    		{
    			count_node2->next = node;
    			node->next = NULL;
    		}
    		else
    		{
    			count_node2->next = node;
    			node->next = count_node1;
    		}
    	}
    	return start1;
    }
    
    
    airline* enter_airline_info(airline *node)             // Function to enter the information about the airline, this function is
    {                                                      // called from the function create_airline_node(airline *start1)by itself.   
    	printf("\n");                                      
    	printf(" Welcome to IGI International Airport\n");
    	printf("Please enter the Airline Name\n");
    	printf("\n");
    	fflush(stdin);
    	node->airlinename = new char [80];
    	gets(node->airlinename);
    	node->node1 = NULL;
    	return node;
    }
    
    airline* delete_airline_node(airline *start)          // Function to delete the name of a airline, function 
    {                                                    // searches for the name and deletes if it is found.
    	if(start1 == NULL)
    	{
    		printf("\n");
    		printf("Sorry, this Airport is not operational at this moment\n");
    	}
    	else
    	{
    		char airlinename[80];
    		printf("\n");
    		printf("Please enter the  name of the Airline you want to delete\n");
    		fflush(stdin);
    		gets(airlinename);
    		airline *count_node1, *count_node2;
    		airline *temp;
    		for(count_node1 = start1; (count_node1 != NULL) && (strcmp(count_node1->airlinename, airlinename) != 0); count_node2 = count_node1, count_node1 = count_node1->next);
    		if(count_node1!= NULL)
    		{
    			if (count_node1 == start1)
    			{
    				temp = start1;
    				start1 = start1->next;
    				free(temp);
    			}
    			else if(count_node1->next == NULL && count_node1 != start1) 
    			{
    				temp = count_node1;
    				count_node2->next = NULL;
    				free (temp);
    			}
    			else
    			{
    				temp = count_node1;
    				count_node2->next = count_node1->next;
    				free (temp);
    			}
    		}
    		else 
    		{
    			printf("\n");
    			printf("Sorry, this airline is currently not in service at this airport\n");
    		} 
    	}
    	return start1;
    }
    
    
    void print_airline_list(airline *start)                       //Function to print all the airlines operating on the airport
    {
    	if (start1 == NULL)
    	{
    		printf("\n");
    		printf("Sorry, this Airport is not operational at this moment\n");
    	}
    	else
    	{
    		printf("\n");
    		airline *count;
    		for (count = start1; count != NULL; count = count->next)
    		printf("%s\n", count->airlinename);
    	}
    }
    
    airline* enter_flight_menu(airline *start1)        // Function to search for the airline entered and enter its flight list menu
    {
    	char airlinename[80];
    	printf("\n");
    	printf("Welcome to the Flight list Menu\n");
    	printf("Enter the Airline name you wish to check\n");
    	fflush(stdin);
    	gets(airlinename);
    	airline *count;
    	for(count = start1; (count != NULL) && (strcmp(count->airlinename, airlinename) != 0); count = count->next);
    	if(count == NULL)
    	{
    		printf("\n");
    		printf("Sorry, this airline does not operate in this airport\n");
    		return start1;
    	}
    	else
    	{
    		printf("\n");
    		count->node1 = flight_menu(count->node1);
    		return start1;
    	}
    }
    
    
    airline* airline_menu(airline *start)                            // Menu Function which is handles the airlinelist
    {                                                                      
    	int choice;
    	printf("Welcome to the Main Menu\n");
    	printf("Please enter your choice from the menu shown below\n");
    	printf("1: Add a new airline to this airport\n");
    	printf("2: Delete an airline from the airport\n");
    	printf("3: Display the Airlines List at this Airport\n");
        printf("4: Enter Flight menu for an airline\n");
    	scanf ("%d", &choice);
    	switch(choice)
    	{
    	case 1: 
    		{ 
    			start1 = create_airline_node(start1);
    		} break;
    	case 2:
    		{  
    			start1 = delete_airline_node(start1);
    		} break;
    	case 3:
    		{
    			print_airline_list(start1);
    		} break;
    	case 4:
    		{
    			start1 = enter_flight_menu(start1);
    		} break;
    	default:
    		{
    			start1 = airline_menu(start1);
    		} break;
    	}
    	printf("\n");
    	start1 = airline_menu(start1);
    	return start1;
    }
    
    
    //----------------------------- MEMBER FUNCTIONS TO MANIPULATE THE FLIGHT LINKED LIST --------------------------------------------
    
    
    flight* create_flight_node(flight *start2)           // Creates a sorted list of flights (default entry sort condition by flight no.)
    {                                                    // by entering the flight node at the sorted position, 
        printf("\n");                                    // it calls the function "enter_flight_info() to ask the 
    	if (start2 == NULL)                              // user for its information
    	{
    		start2 = (flight *) malloc(sizeof(flight));
    		start2 = enter_flight_info(start2);
    		start2->next = NULL;
    	}
    	else
    	{
    		flight *count_node1, *count_node2, *node;
    		node = (flight *) malloc(sizeof(flight));
    		node = enter_flight_info(node);
    		for (count_node1 = start2; (count_node1 != NULL) && (strcmp(count_node1->flightname, node->flightname) <= 0); count_node2 = count_node1, count_node1 = count_node1->next);
    		if(count_node1 == start2)
    		{
    			node->next = start2;
    			start2 = node;
    		}
    		else if (count_node1 == NULL)
    		{
    			count_node2->next = node;
    			node->next = NULL;
    		}
    		else
    		{
    			count_node2->next = node;
    			node->next = count_node1;
    		}
    	}
    	return start2;
    }
    
    
    flight* enter_flight_info(flight *node)               // Function to enter the information about the flight, this function is
    {                                                    // called from the function create_flight_node(flight *start)by itself.   
    	printf(" Welcome to the Flight List\n");
    	printf("Please enter the Flight Name\n");
    	fflush(stdin);
    	node->flightname = new char [80];
    	gets(node->flightname);
    	printf("Please enter the Departure Location\n");
    	fflush(stdin);
    	node->departure_location = new char [80];
    	gets(node->departure_location);
    	printf("Please enter the Arrival Location\n");
    	fflush(stdin);
    	node->arrival_location = new char [80];
    	gets(node->arrival_location);
    	printf("Please enter the Take off time\n");
    	fflush(stdin);
    	node->take_off_time = new char [80];
    	gets(node->take_off_time);
    	node->node2 = NULL;
    	return node;
    }
    
    flight* delete_flight_node(flight *start2)            // Function to delete the name of a flight, function 
    {                                                     // searches for the name and deletes if it is found.
    	printf("\n");
    	if(start2 == NULL)
    	{
    		printf("Sorry, no available Flights today\n");
    	}
    	else
    	{
    		char flightname[80];
    		printf("Please enter the flight name you want to delete\n");
    		fflush(stdin);
    		gets(flightname);
    		flight *count_node1, *count_node2;
    		flight *temp;
    		for(count_node1 = start2; (count_node1 != NULL) && (strcmp(count_node1->flightname, flightname) != 0); count_node2 = count_node1, count_node1 = count_node1->next);
    		if(count_node1!= NULL)
    		{
    			if (count_node1 == start2)
    			{
    				temp = start2;
    				start2 = start2->next;
    				free(temp);
    			}
    			else if(count_node1->next == NULL && count_node1 != start2) 
    			{
    				temp = count_node1;
    				count_node2->next = NULL;
    				free (temp);
    			}
    			else
    			{
    				temp = count_node1;
    				count_node2->next = count_node1->next;
    				free (temp);
    			}
    		}
    		else 
    		{
    			printf("\n");
    			printf("Sorry, this name was not found in this list\n");
    		} 
    	}
    	return start2;
    }
    
    
    void print_flight_list(flight *start2)
    {
    	printf("\n");
    	if (start2 == NULL)
    	{
    		printf("Sorry, the Flight List is empty\n");
    	}
    	else
    	{
    		flight *count;
    		for (count = start2; count != NULL; count = count->next)
    		{
    			printf("%s\n", count->flightname);
    		    printf("From %s\n", count->departure_location);
    		    printf("To %s\n", count->arrival_location);
    		    printf("Take off Time : %s\n", count->take_off_time);
    			printf("\n");
    		}
    	}
    }
    
    flight* enter_passenger_menu(flight *start2)        // Function to search for the flight entered and enter its passenger list menu
    {
    	printf("\n");
    	char flightname[80];
    	printf("Welcome to the passenger list Menu\n");
    	printf("Enter the Flight name you wish to check\n");
    	fflush(stdin);
    	gets(flightname);
    	flight *count;
    	for(count = start2; (count != NULL) && (strcmp(count->flightname, flightname) != 0); count = count->next);
    	if(count == NULL)
    	{
    		printf("Sorry, this flight is not available\n");
    		return start2;
    	}
    	else
    	{
    		count->node2 = passenger_menu(count->node2);
    		return start2;
    	}
    }
    
    flight* flight_menu(flight *start2)                          // Menu Function which is handles the flightlist for an airline
    {                                                                      
    	int choice;
    	printf("Welcome to the Flight menu\n");
    	printf("Please enter your choice from the menu shown below\n");
    	printf("1: Add a new Flight to this Airline\n");
    	printf("2: Delete a Flight from the Airline\n");
    	printf("3: Display the Flight List for the Airline\n");
        printf("4: Enter passenger menu for a flight\n");
    	printf("5: Return back to the Main Menu\n");
    	scanf ("%d", &choice);
    	switch(choice)
    	{
    	case 1: 
    		{ 
    			start2 = create_flight_node(start2);
    		} break;
    	case 2:
    		{  
    			start2 = delete_flight_node(start2);
    		} break;
    	case 3:
    		{
    			print_flight_list(start2);
    		} break;
    	case 4:
    		{
    			start2 = enter_passenger_menu(start2);
    		} break;
    	case 5:
    		{
    			return start2;
    		} break;
    	default:
    		{
    			start2 = flight_menu(start2);
    		} break;
    	}
    	printf("\n");
    	start2 = flight_menu(start2);
    	return start2;
    }
    
    
    //----------------------------- MEMBER FUNCTIONS TO MANIPULATE THE  PASSENGER LINKED LIST --------------------------------------------
    
    
    
    
    passenger* create_passenger_node(passenger *start3)  //Creates a sorted list of passengers by entering the passenger node at the
    {                                                    // sorted position, it calls the function "enter_passenger_info() to
        printf("\n");                                    // ask the user for its information
    	if (start3 == NULL)                              
    	{
    		start3 = (passenger *) malloc(sizeof(passenger));
    		start3 = enter_passenger_info(start3);
    		start3->next = NULL;
    	}
    	else
    	{
    		passenger *count_node1, *count_node2, *node;
    		node = (passenger *) malloc(sizeof(passenger));
    		node = enter_passenger_info(node);
    		for (count_node1 = start3; (count_node1 != NULL) && (strcmp(count_node1->name, node->name) <= 0); count_node2 = count_node1, count_node1 = count_node1->next);
    		if(count_node1 == start3)
    		{
    			node->next = start3;
    			start3 = node;
    		}
    		else if (count_node1 == NULL)
    		{
    			count_node2->next = node;
    			node->next = NULL;
    		}
    		else
    		{
    			count_node2->next = node;
    			node->next = count_node1;
    		}
    	}
    	return start3;
    }
    
    
    passenger* enter_passenger_info(passenger *node)     // Function to enter the name of the passenger, this function is called 
    {                                                    // from the function create_passenger_node(passenger *start)by itself.   
    	printf(" Welcome to the passenger list\n");
    	printf("Please enter your name\n");
    	fflush(stdin);
    	node->name = new char [80];
    	gets(node->name);
    	return node;
    }
    
    passenger* delete_passenger_node(passenger *start3)   // Function to delete the name of a passenger in the flight, function 
    {                                                     // searches for the name and deletes if it is found.
    	printf("\n");
    	if(start3 == NULL)
    	{
    		printf("\n");
    		printf("Sorry, the passenger list is empty\n");
    	}
    	else
    	{
    		char name[80];
    		printf("Please enter the name you want to delete\n");
    		fflush(stdin);
    		gets(name);
    		passenger *count_node1, *count_node2;
    		passenger *temp;
    		for(count_node1 = start3; (count_node1 != NULL) && (strcmp(count_node1->name, name) != 0); count_node2 = count_node1, count_node1 = count_node1->next);
    		if(count_node1!= NULL)
    		{
    			if (count_node1 == start3)
    			{
    				temp = start3;
    				start3 = start3->next;
    				free(temp);
    			}
    			else if(count_node1->next == NULL && count_node1 != start3) 
    			{
    				temp = count_node1;
    				count_node2->next = NULL;
    				free (temp);
    			}
    			else
    			{
    				temp = count_node1;
    				count_node2->next = count_node1->next;
    				free (temp);
    			}
    		}
    		else 
    		{
    			printf("\n");
    			printf("Sorry, this name was not found in this list\n");
    		} 
    	}
    	return start3;
    }
    
    passenger* passenger_menu(passenger *start3)                   // Menu Function which is called from main and takes 
    {                                                              // over the program list after that              
    	printf("\n");                                                     
    	int choice;
    	printf("Welcome to the passenger menu\n");
    	printf("Please enter your choice from the menu shown below\n");
    	printf("1: Add a passenger to this flight\n");
    	printf("2: Delete a passenger from this flight\n");
    	printf("3: Display the passenger list for this flight\n");
    	printf("4: Return back to the Flight Menu\n");
    	scanf ("%d", &choice);
    	switch(choice)
    	{
    	case 1: 
    		{ 
    			start3 = create_passenger_node(start3);
    		} break;
    	case 2:
    		{  
    			start3 = delete_passenger_node(start3);
    		} break;
    	case 3:
    		{
    			print_passenger_list(start3);
    		} break;
    	case 4:
    		{
    			return start3;
    		} break;
    	default:
    		{
    			start3 = passenger_menu(start3);
    		} break;
    	}
    	start3 = passenger_menu(start3);
    	return start3;
    }
    
    
    
    void print_passenger_list(passenger *start3)
    {
    	printf("\n");
    	if (start3 == NULL)
    	{
    		printf("Sorry, the passenger list is empty\n");
    	}
    	else
    	{
    		passenger *count;
    		for (count = start3; count != NULL; count = count->next)
    		printf("%s\n", count->name);
    	}
    }
    
    //--------------------------------- MAIN FUNCTION CALLING THE MENU FUNCTION ------------------------------------------------
    
    void main()
    {
    	start1 = airline_menu(start1);
    }

  2. #2
    Registered User hk_mp5kpdw's Avatar
    Join Date
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    Quote Originally Posted by gemini_shooter
    Now here are my PROBLEMS:

    1. the condition tested in the for loops in the functions given above looks like this

    (count_node1 != NULL) && (strcmp(count_node1->airlinename, node->airlinename) <= 0)

    If i change this condtion to :

    (strcmp(count_node1->airlinename, node->airlinename) <= 0) &&
    (count_node1 != NULL)

    the function doesn't work properly it gives me an error if the second name entered is greater that the first ????????????

    any explantion would be a great help
    I believe conditions are tested left to right. In your first case, this means you are testing if a node exists and only then do you test the values contained in that node with what you are adding/checking. This is good.

    In the second case, you jump right in and test the values contained in a node with what you are attempting to add/check without knowing if the node exists; only after do you check for the existance of the node (and by this time its too late). This is bad. Do you see the potential problem? It really helps to know if a node exists before you attempt to access its values.
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

  3. #3
    Registered User
    Join Date
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    91

    Hmmmmmm.......... interesting

    I understand what you are trying to say, I guess I never noticed this side of it ,

    However it would also never enter that block of else if the list was empty, since there is an if-else around it and that if holds the key for the empty list.

    Hence if it enter's that block a node always exists so there is always a value to check for that node.

    I am a little slow at this stuff .....



    Any idea on how to implement this using files . It would be a great help !!!!

  4. #4
    Registered User hk_mp5kpdw's Avatar
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    Quote Originally Posted by gemini_shooter
    I understand what you are trying to say, I guess I never noticed this side of it ,

    However it would also never enter that block of else if the list was empty, since there is an if-else around it and that if holds the key for the empty list.

    Hence if it enter's that block a node always exists so there is always a value to check for that node.

    I am a little slow at this stuff .....


    I don't know what surrounds your code that might affect that, but what I said could still apply depending on how your code looked, as an example:

    Code:
    if( count_node1 != NULL ) // Start off by making sure we have a node
    {
        while( (count_node1 != NULL) && (strcmp(...,...) <= 0 ) )
            count_node1 = count_node1->next;
        // Do stuff
    }
    The above would still fail once you reached the end of the list if you switched around the condition in the while loop. Yeah you make sure you have a list to begin with, but once you start traversing the list in the while loop, count_node1 could end up NULL and referencing any node members at that point would be potentially disastrous. But again, it all depends on what your code looks like and I haven't looked at your code all that deeply.



    Quote Originally Posted by gemini_shooter
    Any idea on how to implement this using files . It would be a great help !!!!
    What exactly are refering to? Do you mean you wish to save your data to files at the end of the program and to load them up when the program starts? Well, you are going to need to some functions that traverse the lists and store/read them to/from file(s).

    With data members like char* in your nodes, saving/loading to/from files becomes a bit more of a challenge. When saving this type of data, you basically have to write out the length of the data that is to follow first and then you write out the data (characters) itself. This is so when you read the data back in you can read in this length value and dynamically allocate an appropriate size memory chunk followed by reading in the characters themselves.
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

  5. #5
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    Thanks A Lot !!!!

    Your a genius hk_mp5kpdw !!!!!!

    I finally got it and ur absolutely right even if the node exists once it goes to the end it looks for the member of a NULL

    and then DISASTOR STRIKES !!!!!

    About the files a few questions :

    1. Does this file structure sound right to you :

    one file to store the names of all the airlines operating on the airport.

    one file for each airline to store the file names and data

    one file for each flight contaning list of passengers for that flight

    2. Is there a way i can copy the entire struct like write and read in C++, I hope there is

    3. once I close the program and start it again before even reading member like airline name how would i even know its length ????? now Iam lost again

  6. #6
    Registered User hk_mp5kpdw's Avatar
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    Quote Originally Posted by gemini_shooter
    1. Does this file structure sound right to you :

    one file to store the names of all the airlines operating on the airport.

    one file for each airline to store the file names and data

    one file for each flight contaning list of passengers for that flight
    Sounds like a lot of files to me. If I were doing this I would have a single file with a conceptual structure similar to this (indentation is just to make it easier for you to read):

    Code:
    [number of airlines]
    [first airline's name]
        [number of flights for first airline]
        [first airline's, first flight's information]
        [first airline's, first flight's number of passengers]
            [first airline's, first flight's, first passengers information]
            [first airline's, first flight's, next passengers information]
            [etc...]
        [first airline's, second flight's information]
        [first airline's, second flight's number of passengers]
            [first airline's, second flight's, first passenger's information]
            [first airline's, second flight's, next passenger's information]
            [etc...]
        [etc...]
    [second airline's name]
        [etc...]

    Quote Originally Posted by gemini_shooter
    2. Is there a way i can copy the entire struct like write and read in C++, I hope there is
    Not an easy way using a single fwrite/fread call. Saving/reading the values of node pointers themselves would be meaningless. Saving the data pointed to by all your character pointer data members would likely require writing/reading a length value followed by the actual data itself as mentioned in my earlier post.

    As an example, using the rough format described above, here is how I would start this (just showing the writing of the airline data, not any flight or passenger data):

    Code:
    FILE* fp;
    struct airline *temp;
    int count = 0;
    
    // Open file for writing
    fp = fopen("airline.txt","wb");  // Note binary mode
    
    // Determine number of airlines and write to file
    for( temp = start1; temp != NULL; temp = temp->next ) ++count;
    fwrite(&count,sizeof(int),1,fp);
    
    // Loop through and write airlines data to file
    for( temp = start1; temp != NULL; temp = temp->next )
    {
        // Determine length of airline name and write to file
        int length = strlen(temp->name);
        fwrite(&length,sizeof(int),1,fp);
    
        // Write airline name to file
        fwrite(temp->name,length,1,fp);
    
        // Write airline flight information to file
        determine and write number of flights for current airline to file
        for( loop through flights for current airline )
        {
            // Write passenger data to file
            determine and write number of passengers for current flight to file
            for( loop through passengers in current flight )
            {
            }
        }
    }
    
    fclose(fp);
    Parts in blue are more pseudocode.

    Quote Originally Posted by gemini_shooter
    3. once I close the program and start it again before even reading member like airline name how would i even know its length ????? now Iam lost again
    As mentioned, your write routine should have written a length parameter to the file that you would read in first. The write routine above does this writting of a length value. You would then allocate memory of an appropriate size (length + 1) and then perform a second read from the file into this memory buffer.

    As a rough example of the read process:
    Code:
    FILE* fp;
    struct airline *start, *curr, *temp;
    int count;
    
    // Initialize pointers
    start = curr = NULL;
    
    // Open file for reading
    fp = fopen("airline.txt","rb");
    
    // Read in number of airlines stored in file
    if( fp == NULL )
        count = 0;
    else
        fread(&count,sizeof(int),1,fp);
    
    // Loop through "count" airlines
    for( ; count > 0; --count )
    {
        int length;
    
        // read airline name length
        fread(&length,sizeof(int),1,fp);
    
        // allocate room for a single airline structure
        temp = malloc(sizeof(struct airline));
        temp->next = NULL;
        temp->name = malloc(length+1);
    
        // read in airline's name and NULL terminate
        fread(temp->name,length,1,fp);
        temp->name[length] = 0;
    
        // Add current airline to end of growing list of airlines
        if( start == NULL ) start = curr = temp;
        else
        {
            curr->next = temp;
            curr = curr->next;
        }
    
        // Read in flight information for current airline
        read number of flights
        for( loop through number of flights just read in)
        {
            // Read in passenger information
            read number of passengers
            for( loop through number of passengers for current flight)
            {
            }
        }
    }
    Again, parts in blue are just some rough/minimal pseudocode. You'd want to add in more error checking, like verifying all your reads/writes processed the expected amount of data.
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
    -Christopher Hitchens

  7. #7
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    You are the man hk_mp5kpdw , Thanks for the tip or I should say you solved the whole problem for me ..

    Thanks again man !!!

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