Compilare: user.cpp: In function ‘int main()’: user.cpp:31:15: warning: unused variable ‘k’ [-Wunused-variable] int i,j,n,k=0,prev=-1,l=1; ^ user.cpp:31:19: warning: unused variable ‘prev’ [-Wunused-variable] int i,j,n,k=0,prev=-1,l=1; ^~~~ user.cpp:29:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("trapez.in","r",stdin); ^ user.cpp:30:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("trapez.out","w",stdout); ^ user.cpp:34:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &n); ^ user.cpp:37:33: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d", &p.x,&p.y); ^