$ rustc for2.rs 
$ ./for2 
(i,j) = (0,0).
(i,j) = (0,1).
(i,j) = (0,2).
(i,j) = (0,3).
(i,j) = (0,4).
(i,j) = (1,0).
(i,j) = (1,1).
(i,j) = (1,2).
(i,j) = (1,3).
(i,j) = (1,4).
(i,j) = (2,0).
(i,j) = (2,1).
(i,j) = (2,2).
(i,j) = (2,3).
(i,j) = (2,4).
(i,j) = (3,0).
(i,j) = (3,1).
(i,j) = (3,2).
(i,j) = (3,3).
(i,j) = (3,4).
(i,j) = (4,0).
(i,j) = (4,1).
(i,j) = (4,2).
(i,j) = (4,3).
(i,j) = (4,4).