How to pad Fortran floating point output with leading zeros?

Question

I have some floating point numbers that I need to output from a Fortran program. Let\'s say the maximum number could be 999.9999 and they are all non-negative. I need zero

Answer 1

This is a trick I used to use in MS BASIC on the Commodore PETs in the late 70s. The code has been modified for negative numbers. If you would like positive numbers to have a leading +, just change the last character of signchr to '+'

subroutine leadingzero(x)
   real x
   character(len=16) str
   character, dimension(3):: signchr = (/'-', ' ', ' ' /)
   write(str,'(F9.4)') 1000.0 + abs(x)
   write(*,*) signchr(int(sign(1.0,x)) + 2), str(2:) ! drop the 1
end subroutine leadingzero

program main
   call leadingzero(0.01)
   call leadingzero(0.1)
   call leadingzero(2.532)
   call leadingzero(9.9999)
   call leadingzero(9.999999)
   call leadingzero(10.987)
   call leadingzero(123.456)
   call leadingzero(0.0)
   call leadingzero(-0.01)
   call leadingzero(-0.1)
   call leadingzero(-2.532)
   call leadingzero(-9.9999)
   call leadingzero(-9.999999)
   call leadingzero(-10.987)
   call leadingzero(-123.456)
end program

Edit - returning result in a string

subroutine leadingzerostr(x, str_temp)
    real x
    character(*) str_temp
    character(len=10) str
    character, dimension(3):: signchr = (/'-', ' ', ' ' /)
    write(str,'(F10.4)') 10000.0 + abs(x)
    str_temp = str
    str_temp(1:1) = signchr(int(sign(1.0,x)) + 2)
end subroutine leadingzerostr