program f90_10to16
    implicit none
    integer::num
    character(len=2)::answer
    integer::i

    do i=0,255
        num=i
        answer=C10to16(num)
        write(6,*) i,answer
    end do

stop

contains

    character(len=2) function C10to16(num)
        integer,intent(in)::num
        integer,parameter::n=10
        integer::r(1:n)
        integer::i,m
        integer::numd=16
        character(len=1)::snum(1:n)
        character(len=200)::ans
        integer::num0,qq

        num0=num
        do i=1,n
            qq=num0/numd
            r(i)=num0-numd*qq
            if(qq==0)exit
            num0=qq
        end do
        m=i
        do i=m,1,-1
            if(r(i)==10)snum(i)='A'
            if(r(i)==11)snum(i)='B'
            if(r(i)==12)snum(i)='C'
            if(r(i)==13)snum(i)='D'
            if(r(i)==14)snum(i)='E'
            if(r(i)==15)snum(i)='F'
            if(r(i)<=9)then
                write(snum(i),'(i1.1)') r(i)
            end if
        end do
        ans=''
        do i=m,1,-1
            ans=trim(adjustl(ans))//snum(i)
        end do
        if(len_trim(ans)==1)ans='0'//trim(ans)
        C10to16=ans

    end function C10to16

end program f90_10to16