Compilare: user.c: In function ‘main’: user.c:38:3: warning: implicit declaration of function ‘abs’ [-Wimplicit-function-declaration] fprintf( fout, "%.5f\n", 0.5 * abs( area ) ); ^ user.c:26:9: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf( fin, "%d", &N ); ^ user.c:28:11: warning: ignoring return value of ‘fscanf’, declared with attribute warn_unused_result [-Wunused-result] fscanf( fin, "%d%d", &v[i].x, &v[i].y ); ^