implicit none
      integer i,n
      real a,b,h,x,y,xl,yl,f
      real yp,k1,y0
      real err,exact
      character char*11

      print*,' Enter number of intervals n'
      read(5,*) n
      print*,' Enter a,b,y(a)'
      read(5,*) a,b,y0

      h=(b-a)/float(n)


 100  continue
      y=y0
      x=a

      write(6,30) x,y
 30   format(/,' Solving with Euler Method gives:',/,
     &         '   X        Y         exact     %error',
     &         /,1x,f5.3,1x,f10.6,1x,f10.6)


      do i=1,n
        xl=x
        yl=y
        k1=h*f(xl,yl)
        x=xl+h
        y=yl+k1
        exact=2.0*sin(x)*sin(x)+3.*x
        if(abs(exact).gt.1.e-6) then
           err=100.0*(y-exact)/exact
           write(6,2) x,y,exact,err
        else
           char='div by zero'
           write(6,3) x,y,exact,char
        endif

      enddo

 2    format(1x,f6.3,1x,f10.6,1x,f10.6,1x,f10.6)
 3    format(1x,f6.3,1x,f10.6,1x,f10.6,2x,a11)


      stop
      end


      real function f(x,y)
      implicit none
      real x,y
      f=4.0*sin(x)*cos(x)+3.0
      return
      end