foo.cc: In function 'int main()':
foo.cc:8:10: warning: 'a' is used uninitialized in this function [-Wuninitialized]
  for(int i=a; i<b; i++) 
          ^
foo.cc:8:16: warning: 'b' is used uninitialized in this function [-Wuninitialized]
  for(int i=a; i<b; i++) 
               ~^~