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, "%lf %lf", &x2, &y2); ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ main.c:5:22: warning: 'first_y' may be used uninitialized in this function [-Wmaybe-uninitialized] double result = (x1 * y2 - x2 * y1); ~~~^~~~ main.c:21:18: note: 'first_y' was declared here double first_x, first_y; ^~~~~~~ main.c:5:32: warning: 'first_x' may be used uninitialized in this function [-Wmaybe-uninitialized] double result = (x1 * y2 - x2 * y1); ~~~^~~~ main.c:21:9: note: 'first_x' was declared here double first_x, first_y; ^~~~~~~