Styjun

I'm trying to read some numbers in C from a text file which contains 1000 lines of numbers such as:

-340,495,-153,-910,835,-947 
-175,41,-421,-714,574,-645 
-547,712,-352,579,951,-786 
419,-864,-83,650,-399,171 
...

but when I execute the code I see the i variable starts at 901 instead of 0 so it reads the numbers from the point i=901 to i=999. This is where I am experiencing problems.

I've tried to use a while loop instead of a for loop to avoid an extra i variable:

while(!feof(file_in))
 fscanf(file_in,"%d%*c%d%*c",&a[0],&a[1]);
 fscanf(file_in,"%d%*c%d%*c",&b[0],&b[1]);
 fscanf(file_in,"%d%*c%d%*c",&c[0],&c[1]);
 printf("A(%d,%d) I=%dn",a[0],a[1],i);
 printf("B(%d,%d) I=%dn",b[0],b[1],i);
 printf("C(%d,%d) I=%dn",c[0],c[1],i); 

This is the part of the code I'm having hard time with:

int main(void) 
 FILE *file_in;

 int a[2];
 int b[2];
 int c[2];

 file_in = fopen("triangles.txt","r");

 if (file_in == NULL)
 printf("Can't open file for reading.n");
 exit(0);
 
 else
 for(int i=0;i<1000; i++) 
 fscanf(file_in,"%d%*c%d%*c",&a[0],&a[1]);
 fscanf(file_in,"%d%*c%d%*c",&b[0],&b[1]);
 fscanf(file_in,"%d%*c%dn",&c[0],&c[1]);
 printf("A(%d,%d) I=%dn",a[0],a[1],i);
 printf("B(%d,%d) I=%dn",b[0],b[1],i);
 printf("C(%d,%d) I=%dn",c[0],c[1],i); 
 
 fclose(file_in);
 
 return 0;

What I expect:

A(-340,495) I=0 
B(-153,-910) I=0 
C(835,-947) I=0 
A(-175,41) I=1 
...

What I get:

B(-225,-818) I=901 
C(-808,-657) I=901 
A(-279,-34) I=902 
B(-533,-871) I=902 
...

I don't think you've yet demonstrated the problem. This is a minor adaptation of your code, reporting errors to stderr, exiting on an error, and so on.

#include <stdio.h>
#include <stdlib.h>

int main(void)

 int a[2];
 int b[2];
 int c[2];
 const char filename[] = "triangles.txt";
 FILE *file_in = fopen(filename, "r");

 if (file_in == NULL)
 
 fprintf(stderr, "Can't open file %s for reading.n", filename);
 exit(EXIT_FAILURE);
 

 for (int i = 0; i < 1000; i++)
 
 fclose(file_in);
 return 0;

Note that it scrupulously checks the scanning operations, and reports problems if (when?) it encounters them.

Beware of the trailing newline in the format string. When the input is coming from a file, it is OK (not necessary, but OK), but it is a dire UI disaster if a human is ever expected to type the numbers.

Given the data file:

-340,495,-153,-910,835,-947 
-175,41,-421,-714,574,-645 
-547,712,-352,579,951,-786 
419,-864,-83,650,-399,171

I get the output:

A(-340, 495) I=0
B(-153,-910) I=0
C( 835,-947) I=0
A(-175, 41) I=1
B(-421,-714) I=1
C( 574,-645) I=1
A(-547, 712) I=2
B(-352, 579) I=2
C( 951,-786) I=2
A( 419,-864) I=3
B( -83, 650) I=3
C(-399, 171) I=3
Failed to read data for i = 4: r1 = -1, r2 = -1, r3 = -1

The last line appears on standard error, of course; the rest is written on standard output.

I think your problem is not in the code shown, therefore.