Compilare: user.cpp: In function ‘int main()’: user.cpp:8:20: warning: for increment expression has no effect [-Wunused-value] for(i=1;i++<=n;i) ^ user.cpp:4:84: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("alee.in","r",stdin),freopen("alee.out","w",stdout),scanf("%d%d",&n,&m); ^ user.cpp:4:84: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] user.cpp:4:84: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] user.cpp:6:39: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&i,&k),a[i][k]=-1; ^ user.cpp:7:34: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d%d%d",&b,&d,&o,&q); ^