program rtbis_main

      real func, rtbis, x1, x2, xacc
      external func, rtbis

      write (*,*) 'What is the range x1 and x2 and accuracy ?'
      read (*,*) x1, x2, xacc

      write (*,*) 'A root is at ', rtbis(func,x1,x2,xacc),
     & ' with accuracy ', xacc

      end


      function func(x)
      real func, x
c     func = x**3
      func = 7*sin(x) + x
      end