Compilare: user.cpp: In function ‘int main()’: user.cpp:20:24: warning: for increment expression has no effect [-Wunused-value] for (i=1;i<=n;i+2) ^ user.cpp:37:24: warning: for increment expression has no effect [-Wunused-value] for (j=1;j<=n;j+2) ^ user.cpp:58:24: warning: for increment expression has no effect [-Wunused-value] for (i=1;i<=n;i+2) ^ user.cpp:75:24: warning: for increment expression has no effect [-Wunused-value] for (j=2;j<=n;j+2) ^ user.cpp:11:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("sotron.in","r",stdin); ^ user.cpp:12:37: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("sotron.out","w",stdout); ^ user.cpp:13:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%ld",&n); ^ user.cpp:15:49: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] for (j=1;j<=n;j++) scanf("%ld",&a[i][j]); ^