Thread: problems reading input file into two arrays

Hi, it's me again. *waves* I'm having some trouble, and I could really use a fresh set (or sets) of eyes.

This program is supposed to take two lists of integers of the same length ended by -1 and store them in two arrays, x and y, which each have 20 elements. The lists are not necessarily 20 numbers long. There's more after that, but it seems most likely that the problem is in my read_file function:

Code:

#define SENTINEL -1

void read_file(int x[20], int y[20], int *count){
	FILE *fp;
	char filename[80], skip_ch;
	int value, status, i;
	printf("Please enter the file name>> ");
	scanf("%s", &filename);
	scanf("%c", &skip_ch); //eat \n
	fp = fopen(filename, "r");
	status=fscanf(fp, "%d", &value);
	for(i=0; value!=SENTINEL && status==1 && i<20; i++){
		x[i]=value;
		status=fscanf(fp, "%d", &value);
	}//read first line into x[]
	if(status!=1 || value==SENTINEL){
		do{
			fscanf(fp, "%c", &skip_ch);
		}while(skip_ch!='\n');
	}//if status!=1 || value==SENTINEL
	for(i=0; value!=SENTINEL && status==1 && i<20; i++){
		y[i]=value;
		status=fscanf(fp, "%d", &value);
	}//read second line into y[]
	*count=i;
}//read_file

int main()
{
	int x[20], y[20], z[20], count;
	read_file(x, y, &count); //prompts for a file name and reads the file into the two arrays
	multiply_arrays(x, y, z, count); //multiplies x and y and puts the results in z
	display_arrays(x, y, z, count); //displays the three-column table
	z_sqrt(z, count); //computes the sum of z, then displays the sum and its square root
	return 0;
}//main

Here's the output I get on running it:

Code:

teyla:~ quasigreat$ cat lists1.dat
10 2 3 17 18 -1
99 8 26 35 40 -1

teyla:~ quasigreat$ ~quasigreat/a.out
Please enter the file name>> lists1.dat
The sqrt of 0 is   0.00

Help is much appreciated.

You forget "status=fscanf(fp, "%d", &value);"
before starting the second line reading.
You should also check the return of fopen() (what happens if the file cannot be opened?)

Thank you! That's fixed it. In the instructor's executable, entering a filename for a file that doesn't exist causes a segmentation fault, so it's not something I need to worry about in this context. (Needless to say, in real life, it'd be a good idea.)