Thread: C Programming for sine waves drawing

I am writing a C program to display the summation of a number of sine waves, which may be of differing phase, amplitude and frequency. The characteristics of each component wave should be supplied by the user and held in a linked-list as well as the wave resulting from the summation of all the entries. It should be possible for user to:

1. add componet waves
2. delete componet waves
3.edit component wave characteristics

The resulting wave should reflect the contents of the link-list at all times.

*Welcome any ideas or code for this program, I will be constantly update the progress on this program and upload code as well as comments.

So what have you done so far?

Just finished writing the first part of the program. This is the database of the sine wave program basic on LINKED LIST, it is partially working, but for some reasons the program would crash while running the delete function, hope someone can help to solve this problem, I reckon it might to do to some variables, but I have already checked many times.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include <dos.h>
#include <windows.h>

typedef struct data_type               // declare structure for sine_wave database
{
        double amp;
        double freq;
        double phase;
        struct data_type *next;
        struct data_type *former;
} DATA;

DATA *current, *first, *previous, *following;

void print_data(DATA *item)             // function to print current SINE-WAVE details
{                                     // to screen

	if (item==NULL)
	{
		gotoxy(20,5);
		printf("                                        ");
		gotoxy(20,5);
                printf("       END OF THE SINE WAVE LIST        ");
	}
	else
	{
		gotoxy(20,5);
		printf("                                        ");
		gotoxy(20,5);
                printf("            SINE WAVE DATA              ");

                gotoxy(25,10); printf("Amplitude:                           ");
                gotoxy(25,11); printf("Frequency:                       Hz  ");
                gotoxy(25,12); printf("Phase:                           deg ");

                gotoxy(40,10); printf("%9.2lf", item->amp);
                gotoxy(40,11); printf("%9.2lf", item->freq);
                gotoxy(40,12); printf("%9.2lf", item->phase);
	}
}

DATA * add_data(DATA *item)              // add a SINE_WAVE to the end of the linked list
{
        DATA *new_data;

	gotoxy(20,5);
        printf("             Adding a new wave               ");


        new_data = (DATA *) malloc(sizeof(DATA));
        new_data->next = NULL;


        gotoxy(25,10); printf("Amplitude:                           ");
        gotoxy(25,11); printf("Frequency:                       Hz  ");
        gotoxy(25,12); printf("Phase:                           deg ");
        
        gotoxy(40,10); scanf("%lf", &new_data->amp);
        gotoxy(40,11); scanf("%lf", &new_data->freq);
        gotoxy(40,12); scanf("%lf", &new_data->phase);

	if (item != NULL)
        {              
                item->next = new_data;
	}

        return (new_data);
}

DATA * del_data(DATA *item)             // delete data from list
{
        DATA *previous, *following;
        if (item!=NULL)                 //ensure item exists to delete
        {
        previous = item->former;        //assign former and next
        following = item ->next;        //linksto pointers accordingly

        if (previous!=NULL) previous -> next=following;            //reroute around
           
        if (previous!=NULL) following -> former=previous;

        free(item);                     //release the item's memory

        if (previous!=NULL) item=previous;
        else item=following;
}
	return(item);
}

DATA * browse(DATA *item)              // move to next item in list
{

	if (item != NULL)
	{
		item = item->next;
	}

	return (item);
}


DATA * find(DATA *item)             // locate a particular item in the list
{
		gotoxy(20,5);
		printf("      Facility not implemented yet!     ");

		Sleep(1000);

		return (item);
}


int main (void)                       // main function
{
        DATA *first=NULL, *current=NULL, *last=NULL;
	char response;

	system("cls");

	do                                 // repeat until "q" hit
	{

                print_data(current);             // print current item in list to screen

                gotoxy(25,19); printf("'d': Delete current inputted data");   // display command options
                gotoxy(25,18); printf("'a': Adding a new sine wave data");
                gotoxy(25,20); printf("'f': find");
		gotoxy(25,21); printf("'w': brouwse the database");
		gotoxy(25,22); printf("'r': return to start of list");
		gotoxy(25,23); printf("'q': quit the database");

		gotoxy(40,25); putch(' ');      // overwrite old command
		gotoxy(25,25);
		printf("Enter command: ");      // get new command
		response = getch();
		gotoxy(34,40); putch(response); // print new command to screen

		switch (response)               // call relevent function
		{
                        case 'd': current = del_data(current); break;
                        case 'a': last = add_data(last); break;
                        case 'f': current = find(first); break;
                        case 'w': current = browse(current); break;
			case 'r': current = first; break;
		}

		if (first == NULL) current = first = last;  // assign pointers to first
									  // item provided in list
	} while (response != 'q');

	system("cls");

	return 0;

}

> gotoxy(34,10); scanf("%5.2lf", new_data->amp);
> gotoxy(34,11); scanf("%9.2lf", new_data->freq);
> gotoxy(34,12); scanf("%5.2lf", &new_data->phase);

Try:

Code:

        gotoxy(34,10); scanf("%lf", &new_data->amp);
        gotoxy(34,11); scanf("%lf", &new_data->freq);
        gotoxy(34,12); scanf("%lf", &new_data->phase);

Thanks for the reply of codse. I am kind of understanding how the delete function work, so I have adapted your code for my program in order to get it working.