/*
Programmazione II - Esempio di codice
<![CDATA[
Example code: linked list demonstration. (20000808 prelz@mi.infn.it)
*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
/* Let's use a simpler structure */
typedef struct measurement_s
{
double value;
char comments[120];
struct measurement_s *next;
} measurement;
#define SAFE_ASSIGN(string,value) \
(string)[sizeof(string)-1] = '\000'; \
strncpy((string),value,sizeof(string)-1);
int
main(int argc, char *argv[])
{
char in[800]; /* Generic input storage */
int record_count = 0;
measurement *record_head = NULL;
measurement *record_tail = NULL;
measurement *new_record;
measurement *cur_record, *next_record;
double old_average, average=0, nvariance=0, variance;
int i;
for (;;)
{
/* Infinite data entry loop. Will exit with break. */
printf ("********* Now processing record # %d.\n",record_count+1);
printf ("Would you like to add a new record ? (Y/N): ");
fgets(in, sizeof(in), stdin);
if (in[0] != 'y' && in[0] != 'Y') break;
new_record = (measurement *)malloc(sizeof(measurement));
if (new_record == NULL)
{
fprintf(stderr,"Warning: Out of Memory.\n");
continue;
}
printf ("Measurement value --->");
fgets(in, sizeof(in), stdin);
new_record->value = atof(in);
printf ("Any comments ? --->");
fgets(in, sizeof(in), stdin);
in[strlen(in)-1] = '\000'; /* Remove trailing newline */
SAFE_ASSIGN(new_record->comments,in);
printf ("\n\nI have the following data:\n");
printf ("Meas. value: %g\n", new_record->value);
printf ("Comments: %s\n", new_record->comments);
printf ("\nIs it OK to store these data ? (Y/N): ");
fgets(in, sizeof(in), stdin);
if (in[0] != 'y' && in[0] != 'Y')
{
free(new_record); /* This is very important!! */
continue;
}
printf("\n");
record_count++;
/* Append to the linked list tail */
if (record_tail != NULL)
{
record_tail->next = new_record;
}
record_tail = new_record;
/* Set head pointer if necessary */
if (record_head == NULL) record_head = new_record;
}
/* Let's now loop over the collected data */
for (i=0,cur_record = record_head; cur_record!=NULL;
i++,cur_record = cur_record->next)
{
printf ("\n********* Record # %d.\n\n",i+1);
printf ("Meas. value: %15.13g\n", cur_record->value);
printf ("Comments: %s\n", cur_record->comments);
/* Compute average and std. deviation values */
old_average = average;
average = (double)i/(double)(i+1)*average +
(double)1/(double)(i+1)*cur_record->value;
nvariance = (double)1/(double)(i+1) *
( (double)(i) * nvariance + pow(cur_record->value,2) +
(double)i * pow(old_average,2) -
(double)(i+1) * pow(average,2) );
if (i > 0) variance = (double)(i+1)*nvariance/(double)i;
else variance = nvariance;
printf ("Current average: %15.13g\n",average);
printf ("Current std dev: %15.13g\n",sqrt(variance));
}
printf("\n");
/* Destroy and free the list */
for (cur_record = record_head; cur_record!=NULL;
cur_record = next_record)
{
next_record = cur_record->next;
free(cur_record);
}
exit(0);
}
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