/in/foo.cc: In function 'int main()':
/in/foo.cc:24:8: warning: statement has no effect [-Wunused-value]
  for( i; i<n+m; i++)
        ^
/in/foo.cc: In function 'void merge(std::vector<int>, int, int)':
/in/foo.cc:47:12: warning: unused variable 'k' [-Wunused-variable]
  int j=m+1,k=0;
            ^
/in/foo.cc:48:6: warning: unused variable 'len' [-Wunused-variable]
  int len=right-left+1;
      ^~~