Fortran - Nested Loops

You can use one or more loop construct inside any another loop construct. You can also put labels on loops.

Syntax

iloop: do i = 1, 3
   print*, "i: ", i
   
   jloop: do j = 1, 3         
      print*, "j: ", j         
      
      kloop: do k = 1, 3
         print*, "k: ", k
         
      end do kloop
   end do jloop  
end do iloop

Example

program nestedLoop 
implicit none

   integer:: i, j, k
   
   iloop: do i = 1, 3      
      jloop: do j = 1, 3         
         kloop: do k = 1, 3              
         
            print*, "(i, j, k): ", i, j, k               
            
         end do kloop       
      end do jloop
   end do iloop

end program nestedLoop  

When the above code is compiled and executed, it produces the following result −

 (i, j, k):            1           1           1
 (i, j, k):            1           1           2
 (i, j, k):            1           1           3
 (i, j, k):            1           2           1
 (i, j, k):            1           2           2
 (i, j, k):            1           2           3
 (i, j, k):            1           3           1
 (i, j, k):            1           3           2
 (i, j, k):            1           3           3
 (i, j, k):            2           1           1
 (i, j, k):            2           1           2
 (i, j, k):            2           1           3
 (i, j, k):            2           2           1
 (i, j, k):            2           2           2
 (i, j, k):            2           2           3
 (i, j, k):            2           3           1
 (i, j, k):            2           3           2
 (i, j, k):            2           3           3
 (i, j, k):            3           1           1
 (i, j, k):            3           1           2
 (i, j, k):            3           1           3
 (i, j, k):            3           2           1
 (i, j, k):            3           2           2
 (i, j, k):            3           2           3
 (i, j, k):            3           3           1
 (i, j, k):            3           3           2
 (i, j, k):            3           3           3