foo.cc: In function 'int main()':
foo.cc:11:6: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
 scanf("%d",&n);
 ~~~~~^~~~~~~~~
foo.cc:12:23: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
 for(i=0;i<n;i++) scanf("%d%d",&a[i],&a[i]);
                  ~~~~~^~~~~~~~~~~~~~~~~~~~