Compilare: user.cpp: In function ‘int main()’: user.cpp:5:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("aria.in","r",stdin); ^ user.cpp:6:35: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("aria.out","w",stdout); ^ user.cpp:9:19: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d",&n); ^ user.cpp:11:40: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d%d",&a[i][1],&a[i][2]); ^ user.cpp:15:33: warning: array subscript is above array bounds [-Warray-bounds] s=s+a[i][1]*a[i+1][2]-a[i+1][1]*a[i][2]; ~~~~~~~~^ user.cpp:15:51: warning: array subscript is above array bounds [-Warray-bounds] s=s+a[i][1]*a[i+1][2]-a[i+1][1]*a[i][2]; ~~~~~~^ user.cpp:17:31: warning: array subscript is above array bounds [-Warray-bounds] s=s+a[i][1]*a[1][2]-a[1][1]*a[i][2]; ~~~~~~^ user.cpp:17:47: warning: array subscript is above array bounds [-Warray-bounds] s=s+a[i][1]*a[1][2]-a[1][1]*a[i][2]; ~~~~~~^