title: SAS date difference
body: <p>what is wrong in below code</p>
  
  <pre><code>%let a='2017-01-01';
  %let b='2017-12-01';
  
  
  %let days = %sysfunc(intck(month,"&amp;a"d,"&amp;b"d));
  %put days;
  </code></pre>
  
  <p>Below is the error</p>
  
  <pre><code>ERROR: Argument 2 to function INTCK referenced by the %SYSFUNC or %QSYSFUNC macro function is not a number.
  ERROR: Argument 3 to function INTCK referenced by the %SYSFUNC or %QSYSFUNC macro function is not a number.
  ERROR: Invalid arguments detected in %SYSCALL, %SYSFUNC, or %QSYSFUNC argument list.  Execution of %SYSCALL statement or %SYSFUNC 
      or %QSYSFUNC function reference is terminated.
  67         %put days;
  days
  </code></pre>