.model small
.stack 100h
.data
    m1 db 'Nhap: $'
    m2 db 10, 13, '$'
    m3 db 'Tong cua '
    a   db ?
        db '+'
    b   db 0
        db '='
    sum db -48, '$'
.code
    begin:
        mov ax, @data
        mov ds, ax

        ;In chuoi "Nhap: "
        lea dx, m1
        mov ah, 9
        int 21h

        ;Doi nhap gia tri vao bien a
        mov ah, 1
        int 21h
        mov a, al

        ;Xuong hang
        lea dx, m2
        mov ah, 9
        int 21h

        ;In chuoi "Nhap: "
        lea dx, m1
        int 21h

        ;Doi nhap gia tri vao bien a
        mov ah, 1
        int 21h
        mov b, al

        ;Thuc hien phep cong
        call cong

        ;Xuong hang
        lea dx, m2
        mov ah, 9
        int 21h

        ;In chuoi "Tong cua a+b=sum"
        lea dx, m3
        int 21h


        mov ah, 4ch
        int 21h

        cong proc
            push ax
            mov al, a
            add al, b
            add sum, al
            pop ax
            ret
        cong endp

    end begin