Thread: Reading Input from a file, line-by-line

For an assignment in my C course, I need to write a program that reads lines of numbers from a file, sorts them, writes the output to a file then reads the next line and continues, until a -1 is reached in the file.

My question is: how would I go about doing this? Or, rather, which functions should I use to read the file as such. The pseudocode for what I want to do is:
Open File
Read (Line until end of line is reached)
Convert each number read into int, then put it into a 1-dimensional array
Do the sorting ('Pancake sorting', if you want to know)
Write the output to a file.
Read in the next line and repeat the sequence.

I'm not exactly sure how to read the file and pick out the numbers from a string, and, moreso, how to make it start reading from a specific line in the file.

(Note: Not asking for you to write the program for me, I'm just asking for help filling in the metaphorical blanks.)

How should I go about having it so it picks up where it left off after sorting each line? I was thinking something along the lines of this:

While (!= EOF)
fgets (numbers, converts to int, puts it into temparray[n])
if (end of line)
sort(temparray [n])
Arraycount = 0

So, it goes through the file, puts the first line into the array, sorts the array, then, if it hasn't reached the end of the file, it resets the array count and starts over again on the next line.

Ok, here's what I've got. As per my assignment instructions, it actually just uses I/O redirection. However, I'm having some errors:

Code:

#include <stdio.h>
char input [30];
int stack [30];
char c;
int cnt = 0;

int main ()
{
        while ((c = getchar()) != '-1')
        {
                if (c != '\n')
                {
                        input[cnt++] = c;
                }
                if (c == '\n')
                {
                        puts(input);
                        printf("Flip would be here.\n");
                        cnt = 0;
                }
        }
}

Input.txt is as follows:

Code:

1 4 7 5 2 5 
8 5 3 2 6 4 1 2 9 10 2
6 9 16 8 4
-1

And the output is:

Code:

1 4 7 5 2 5 
Flip would be here.
8 5 3 2 6 4 1 2 9 10 2
Flip would be here.
6 9 16 8 44 1 2 9 10 2
Flip would be here.
-19 16 8 44 1 2 9 10 2
Flip would be here.
Segmentation fault

So, the problem here is that it seems to keep reading after it hits -1, and it doesn't clear the string. What am I missing here?

So, how would I convert '-' and '1' to an integer? Or, rather should I change it to just

Code:

while ((c = getchar()) != '-')

, since the only reason a '-' would occur would be to denote the '-1'?