This example is meant as a helpfull guide to see how Fortran looks in practice. And will show how to use subroutines, precision and simple arithmetic functions in fortran.
Main
program main
implicit none
call menu()
end program main
The line 'implicit none' is needed in Fortran to avoid obscure errors when defining variables. In earlier Fortran versions all variables were implicitly given as floats (real) unless the first letter in the name between i and n. 'implicit none' makes sure all variables have to be given-type explicit
MenuExpand source
recursive subroutine menu() !'recursive' is needed if the subroutine or function will call itself either directly or implicit
integer :: choice
logical :: valid !A boolean to indicate if the input is valid (.TRUE. or .FALSE.)
print *, '--------------------'
print *, '-----Calculator-----'
print *, '--------------------'
print *, 'Addition 1'
print *, 'Subtraction 2'
print *, 'Multiplication 3'
print *, 'Division 4'
print *, 'High precision division 5'
print *, 'Power 6'
print *, 'Terminate 0'
valid = .FALSE. !Make shure the while loop runs atleast once
do while (.NOT.valid)
read *, choice
valid = .TRUE.
if (choice == 1) then
call addition()
else if (choice == 4) then
call division()
else if (choice == 5) then
call hp_division()
else if (choice == 6) then
call power()
else if (choice == 0) then
print *, 'Program finished'
else
print *, 'False input, please enter valid input: '
valid = .FALSE.
end if
end do
end subroutine menu
The subroutine for addition:
AdditionExpand source
recursive subroutine addition()
implicit none
real :: a,b
print *, 'Enter two numbers to add'
read *, a,b
print *, 'Result: ', a+b
call menu()
end subroutine addition
DivisionExpand source
recursive subroutine division()
implicit none
real :: a,b,res
print *, 'Enter two numbers to divide'
read *, a,b
res = a/b
print *, 'Result: ', res
call menu()
end subroutine division
High precision additionExpand source
recursive subroutine hp_division()
implicit none
integer, parameter :: ikind=selected_real_kind(p=12)
real(kind=ikind) :: a,b,res
print *, 'Enter two numbers to divide'
read *, a,b
res = a/b
print *, 'Result: ', res
call menu()
end subroutine hp_division
PowerExpand source
recursive subroutine power()
implicit none
real :: base, pow
print *, 'Enter base then power'
read *, base, pow
print *, 'Result: ', base**pow
call menu()
end subroutine power