Update ch04-02-do.md

Author: Euler-37

src/ch04-02-do.md

@@ -143,9 +143,17 @@ print *, result_sin
 ``` fortran
 program main
   implicit none
-  !integer::i
+  integer::i
+  integer::a(4)
+  a=[(i,i=1,4)]
+  write(*,*)a
+end program main
+```
+请读者自己尝试运行
+``` fortran
+program main
+  implicit none
   integer::a(4)
-  !a=[(i,i=1,4)]
   a=[(j,integer::j=1,4)] !也可以内部定义循环变量，目前`gfortran`不支持，`ifx,ifort,flang`支持
   write(*,*)a
 end program main