up-to-low-to-up.asm

; assembling using FASM on DOSBox
; fasm.exe utltu.asm
; utltu.com
;
; (c) 2021 Febriyanto Nugroho <[email protected]>

org 100h

        mov     ah, 09h
        mov     dx, pesan
        int     21h

        mov     ah, 0ah
        mov     dx, buffer
        int     21h

        mov     ah, 09h
        mov     dx, pesan2
        int     21h

        mov     bx, buffer+2
    .loop:
        cmp     byte [bx], 00dh
        je      exit

        mov     dl, [bx]
        cmp     dl, "a"
        ja      .uppercase
        cmp     dl, "Z"
        jb      .lowercase
        je      .lowercase
.uppercase:
        and     dl, 0dfh
        mov     ah, 02h
        int     21h

        inc     bx
        jmp     .loop
.lowercase:
        xor     dl, 20h
        mov     ah, 02h
        int     21h

        inc     bx
        jmp     .loop

     exit:
        mov     ax, 4c00h
        int     21h



pesan   db "input : $"
pesan2  db 13, 10, "output : $"
buffer  db ?