Compilare: user.cpp: In function ‘int main()’: user.cpp:51:49: warning: unused variable ‘c2’ [-Wunused-variable] int a2=t[j].y2-t[j].y1,b2=t[j].x2-t[j].x1,c2=-t[j].x1*t[j].y2+t[j].y1*t[j].x2; ^ user.cpp:49:48: warning: unused variable ‘c1’ [-Wunused-variable] int a1=t[i].y2-t[i].y1,b1=t[i].x2-t[i].x1,c1=-t[i].x1*t[i].y2+t[i].y1*t[i].x2; ^ user.cpp:41:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("geometry.in","r",stdin); ^ user.cpp:42:39: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("geometry.out","w",stdout); ^ user.cpp:44:19: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d",&n); ^ user.cpp:46:84: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] for (int i=1;i<=n;i++) scanf("%d %d %d %d",&t[i].x1,&t[i].y1,&t[i].x2,&t[i].y2); ^