foo.cc: In function 'int main()':
foo.cc:24:6: error: redeclaration of 'int y1'
  int y1=2; 
      ^~
foo.cc:15:11: note: 'int y1' previously declared here
  int i=10,y1=y;
           ^~
foo.cc:23:6: warning: unused variable 'nn' [-Wunused-variable]
  int nn=sqrt(y);
      ^~