title: What does the intrinsic function "INDEX" in Fortran 77 do?
body: <p>I am studying a code and came across the following line: </p>
  
  <pre><code>NP = INDEX (PATH, ' ')-1
  </code></pre>
  
  <p>"NP" is declared as an integer variable and PATH as a character. The word "INDEX" stands for a Fortran function (it appears highlighted in the code).</p>
  
  <p>What does it mean and what does it do? I've searched online for help but none of the results I found were satisfactory. </p>
  
  <p>I did find a reference that says the INDEX feature is always written as "INDEX (STRING, SUBSTRING)", but it said nothing more; ergo, the doubt still prevails.</p>
  
  <p>I'd be grateful if you could explain how the code line above works, or if you point me out in the direction of some good resources. </p>