title: Using a variable in Fortran's SYSTEM subroutine
body: <p>How do I use a variable in the command executed in a <code>system</code> subroutine call? For example, if I want to create multiple directories like <code>test_1_1</code>, <code>test_1_2</code>, and so on till <code>test_3_3</code> then what should my code be?</p>
  
  <p>I am trying the following code but can't seem to figure out what to write in #### part. </p>
  
  <pre><code>integer  :: i,j
  
  do i = 1,3
     do j = 1,3 
        CALL system('mkdir folder ####') 
     enddo
  enddo
  </code></pre>