Ignoring # comments in the input for a C program - c

Question

I'm trying to write a program which will read from text files and then output the minimum, maximum and average values. The trouble I am having is ignoring comments in the text files that begin with a hashtag. Here is my working code so far. Can anyone help?
#include <stdio.h>
#include <stdlib.h>
int main( void )
{
char ch, filename[20];
FILE *lun;
int num, min, max, sum, count, first;
printf("Please enter the name of file to load:");
scanf ("%s", filename);
lun=fopen(filename, "r");
if ( lun != NULL)
{
for ( sum= count= first= 0; fscanf( lun, "%d", &num ) == 1; sum += num, ++count )
if ( !first ) { min= max= num; first= 1; }
else if ( num > max ) max= num;
else if ( num < min ) min= num;
fclose( lun );
printf( " Minimum value: %d\n Maximum value: %d\n Average value: %lf\n",
min, max, sum / (double) count );
}
else
printf( "Unable to read file.\n" );
return 0;
}

Answer 1

Read the data in lines (use fgets()).
If the line contains a #, terminate the string there by replacing the '#' with '\0'. Then scan the line for numbers.
See also How to use sscanf() in loops?
And don't forget to check that the file was opened.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void)
{
char filename[20];
printf("Please enter the name of file to load: ");
if (scanf("%19s", filename) != 1)
{
fprintf(stderr, "Failed to read file name\n");
return 1;
}
FILE *lun = fopen(filename, "r");
if (lun == NULL)
{
fprintf(stderr, "Failed to open file %s for reading\n", filename);
return 1;
}
char line[4096];
int min = 0; // Avoid compilation warnings (may be used uninitialized)
int max = 0; // Ditto
int sum = 0;
int count = 0;
while (fgets(line, sizeof(line), lun) != NULL)
{
char *hash = strchr(line, '#');
if (hash != NULL)
*hash = '\0';
int pos;
int num;
int off = 0;
while (sscanf(line + off, "%d%n", &num, &pos) == 1)
{
if (count == 0)
min = max = num;
if (num > max)
max = num;
if (num < min)
min = num;
sum += num;
count++;
off += pos; // Skip through line
}
}
fclose(lun);
printf("Minimum value: %d\nMaximum value: %d\nAverage value: %lf\n",
min, max, sum / (double)count);
return 0;
}
If your compiler doesn't support C99 or later, you will have to move variable declarations to the start of a block (immediately after a {).
Handling doubles isn't really any harder:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(void)
{
char filename[20];
printf("Please enter the name of file to load: ");
if (scanf("%19s", filename) != 1)
{
fprintf(stderr, "Failed to read file name\n");
return 1;
}
FILE *lun = fopen(filename, "r");
if (lun == NULL)
{
fprintf(stderr, "Failed to open file %s for reading\n", filename);
return 1;
}
char line[4096];
double min = 0.0; // Avoids 'used when uninitialized' warnings
double max = 0.0; // Avoids 'used when uninitialized' warnings
double sum = 0;
int count = 0;
while (fgets(line, sizeof(line), lun) != NULL)
{
char *hash = strchr(line, '#');
if (hash != NULL)
*hash = '\0';
int pos;
double num;
int off = 0;
while (sscanf(line + off, "%lf%n", &num, &pos) == 1)
{
if (count == 0)
min = max = num;
if (num > max)
max = num;
if (num < min)
min = num;
sum += num;
count++;
off += pos; // Skip through line
}
}
fclose(lun);
printf("Minimum value: %f\nMaximum value: %f\nAverage value: %f\n",
min, max, sum / count);
return 0;
}