program ex612
  implicit none
  external f1,f2
  intrinsic sin
  real s1,s2,s3,f,integral
  s1=integral(f1,1.0,5.0,20)
  print*,'s1=',s1
  s2=integral(f2,0.0,2.0,10)
  print*,'s2=',s2
  s3=integral(sin,0.4,2.5,10)
  print*,'s3=',s3
end program
function f1(x)
  real f1,x
  f1=sin(x)*sqrt(x)
end
function f2(x)
  real f2,x
  f2=cos(x)/(x+1.0)
end

function integral(f,a,b,n)
  implicit none
  integer:: n,i
  real a,b,f,h,sum,integral
  h=(b-a)/n
  sum=(f(a)+f(b))/2
  do i=1,n-1
    sum=sum+f(a+i*h)
  end do
  integral=sum*h
end