Question

So if I have a file with several numbers, and I open the file using

fp = fopen (filename, "r");

So now I can read the contents of the file correct? How could I do something with the file. Like in this file there are numbers and I want to be able to add them up.

fscanf(fp) 

would be the beginning of what is supposed to be correct? But I am not sure what to do beyond it. What code represents the items inside the file I am opening? If it is “x” then I want to add all the “x”‘s up and then divide it by the total number of files there are.

How can I use the variables inside a file and do things with them?

---

Edited code:

if (fp != NULL)
{
     while (fscanf(fp, "%lf", &d) == 1)
     sum += d;
     mean = sum / total;

     printf ("The number of data values read from this file was %.0lf\n", total);
     printf ("\n%.2lf\n", mean);

     fclose(fp);
}

---

if (fp != NULL)
{
    do
    {
        c = fgetc(fp);
        if (c != EOF)
        {
            if ((char)c == '\n')
            total++;
        }
    } while (feof(fp) == 0);

Answer 1

If the only content in the file is valid numbers, this will work. Actually, it will work until the first text that isn’t a valid number:

#include <stdio.h>

int main(void)
{
    double sum = 0.0;
    char const *filename = "data.file";
    FILE *fp = fopen(filename, "r");
    if (fp != 0)
    {
        double d;
        while (fscanf(fp, "%lf", &d) == 1)
            sum += d;
        fclose(fp);
    }
    printf("%g\n", sum);
    return(0);
}

As a general rule, if a function opens a file successfully, it should close it when it’s finished. In this example, the system would close the file anyway, but it is as well to get into good habits. With a little more care and attention, you could distinguish between a format error (return value of 0 from fscanf()) and EOF or I/O error.