foo.cc:10:4: error: ‘N’ was not declared in this scope
   10 | }a[N];
      |    ^
foo.cc: In function ‘int main()’:
foo.cc:22:22: error: ‘a’ was not declared in this scope
   22 |                 cin>>a[i].m>>a[i].v;
      |                      ^
foo.cc:26:14: error: ‘a’ was not declared in this scope
   26 |         sort(a,a+n,cmp);
      |              ^