How to fix solution with double integration - fortran

Question

The solution for this double integration is -0.083 but in the final compliation it appears -Infinity. It seems that the error is very simple, but I really can't find it.
I have been searching specially in the module section but I don't see why it appears like -Infinity. For example, if you change the two functions between them (x in f2 and x^2 in f1) the solution for the integration is 0.083 and the code gives it correct. Can annyone find the error? Thanks a lot.
module funciones
contains
function f(x,y)
implicit none
real*8:: x,y,f
f=2d0*x*y
end function
function f1(x)
real*8::x,f1
f1=x
end function
function f2(x)
real*8::x,f2
f2=x**2d0
end function
function g(x,c,d,h)
implicit none
integer::m,j
real*8::x,y,c,d,k,s,h,g
m=nint(((d-c)/h)+1d0)
k=(d-c)/dble(m)
s=0.
do j=1d0,m-1d0
y=c+dble(j)*k
s=s+f(x,y)
end do
g=k*(0.5d0*(f(x,c)+f(x,d))+s)
return
end function
subroutine trapecio(a,b,n,integral)
implicit none
integer::n,i
real*8::a,b,c,d,x,h,s,a1,a2,b1,b2,integral
h=(b-a)/dble(n)
s=0d0
do i=1d0,n-1d0
x=a+dble(i)*h
c=f1(x)
d=f2(x)
s=s+g(x,c,d,h)
end do
a1=f1(a)
a2=f2(a)
b1=f1(b)
b2=f2(b)
integral=h*(0.5d0*g(a,a1,a2,h)+0.5d0*g(b,b1,b2,h)+s)
end subroutine
end module
program main
use funciones
implicit none
integer::n,i
real*8::a,b,c,d,x,s,h,integral
print*, "introduzca los valores de a, b y n"
read(*,*) a, b, n
call trapecio (a,b,n,integral)
print*,integral
end program
The main program is simple, just calling the subroutine and using the module. It also prints the final result.

Answer 1

First of all, like mentioned in the comments: your problem is not clear. Which input parameters a, b and n do you use and which result do you expect?
Other than that: the code you posted used deprecated features and non-standard types and bad code style.
Some general hints:
real*8 is non-standard Fortran. Use real(real64) instead. real64 has to be imported by use :: iso_fotran_env, only: real64.
non-integer expressions (do i=1d0,n-1d0) in do-loops are a deleted feature in modern Fortran. Use integers instead.
code should be formatted with white spaces and indentations
print*, should be replaced with write(*,*)
code should always use English names
write implicit none in the beginning of the module, not for every function.
make the module/program interface clear by using the statements private, public, and only
if You want to convert to type real, use the function REAL instead of DBLE
I prefer the cleaner function definition using result
use intent keywords: intent(in) passes the variable as a const reference.
the variables c,d,x,s,h in the main program are unused. Compile with warnings to detect unused variables.
This is the code changed with the suggestions I made:
module funciones
use :: iso_fortran_env, only: real64
implicit none
private
public :: trapecio, r8
integer, parameter :: r8 = real64
contains
function f(x,y) result(value)
real(r8), intent(in) :: x,y
real(r8) :: value
value = 2._r8*x*y
end function
function f1(x) result(value)
real(r8), intent(in) :: x
real(r8) :: value
value = x
end function
function f2(x) result(value)
real(r8), intent(in) :: x
real(r8) :: value
value = x**2._r8
end function
function g(x,c,d,h) result(value)
real(r8), intent(in) :: x, c, d, h
real(r8) :: value
real(r8) :: y, k, s
integer :: m, j
m = NINT(((d-c)/h)+1._r8)
k = (d-c)/REAL(m, r8)
s = 0._r8
do j = 1, m-1
y = c + REAL(j,r8)*k
s = s + f(x,y)
end do
value = k*(0.5_r8*(f(x,c)+f(x,d))+s)
end function
subroutine trapecio(a, b, n, integral)
real(r8), intent(in) :: a, b
integer, intent(in) :: n
real(r8), intent(out) :: integral
integer :: i
real(r8) :: c, d, x, h, s, a1, a2, b1, b2
h = (b-a)/REAL(n,r8)
s = 0._r8
do i = 1, n-1
x = a + REAL(i,r8)*h
c = f1(x)
d = f2(x)
s = s + g(x,c,d,h)
end do
a1 = f1(a)
a2 = f2(a)
b1 = f1(b)
b2 = f2(b)
integral = h*(0.5_r8*g(a,a1,a2,h) + 0.5_r8*g(b,b1,b2,h) + s)
end subroutine
end module
program main
use funciones, only: trapecio, r8
implicit none
integer :: n,i
real(r8) :: a,b,integral
write(*,*) "introduzca los valores de a, b y n"
read(*,*) a, b, n
call trapecio (a,b,n,integral)
write(*,*) integral
end program