Compilare: main.c: In function 'main': main.c:23:2: warning: ignoring return value of 'fscanf', declared with attribute warn_unused_result [-Wunused-result] fscanf(in, "%d", &n); ^~~~~~~~~~~~~~~~~~~~ main.c:25:3: warning: ignoring return value of 'fscanf', declared with attribute warn_unused_result [-Wunused-result] fscanf(in, "%d %d", &x2, &y2); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c:5:18: warning: 'first_y' may be used uninitialized in this function [-Wmaybe-uninitialized] int result = x1 * y2 - x2 * y1; ~~~^~~~ main.c:21:15: note: 'first_y' was declared here int first_x, first_y, check = 0; ^~~~~~~ main.c:5:28: warning: 'first_x' may be used uninitialized in this function [-Wmaybe-uninitialized] int result = x1 * y2 - x2 * y1; ~~~^~~~ main.c:21:6: note: 'first_x' was declared here int first_x, first_y, check = 0; ^~~~~~~