.model small
.stack 100h
.data
welcomeMessage db "Ax^2 + Bx + C = 0", 10, 13, '$'
GiveMeA db "A = $"
GiveMeB db "B = $"
GiveMeC db "C = $"

leng dw 0
minus dw 0
dot dw 0
.code

InputReader PROC
    mov ax, 0
    mov leng, ax
    mov minus, ax
    mov dot, ax

    getchar:
        mov ah, 08h
        int 21h

        cmp al, 13
        jnz goto1
            jmp getchar_stop
        goto1:

        cmp al, 8
        jz backspace_pressed

        cmp al, '-'
        jz minus_pressed

        cmp al, '.'
        jz dot_pressed

        cmp al, '0'
        jb getchar

        cmp al, '9'
        ja getchar

        push ax
        mov dl, al
        mov ah, 02h
        int 21h
        pop ax

        sub al, '0'
        xor ah, ah
        push ax

        mov ax, leng
        inc ax
        mov leng, ax

        mov ax, dot
        cmp ax, 0
        jz getchar

            inc ax
            mov dot, ax

        jmp getchar

    dot_pressed:

        mov ax, dot
        cmp ax, 0
        jnz getchar

        mov ax, minus
        cmp ax, 1
        jz already_minus
            mov ax, leng
            cmp ax, 1
            jb getchar

            mov dl, '.'
            mov ah, 02h
            int 21h

            mov ax, leng
            inc ax
            mov leng, ax

            mov ax, dot
            inc ax
            mov dot, ax

            jmp getchar
        already_minus:
            mov ax, leng
            cmp ax, 2
            jb getchar

            mov dl, '.'
            mov ah, 02h
            int 21h

            mov ax, leng
            inc ax
            mov leng, ax

            mov ax, dot
            inc ax
            mov dot, ax

            jmp getchar
    backspace_pressed:

    minus_pressed:
        mov ax, minus
        cmp ax, 1
        jnz goto2
            jmp getchar
        goto2:

        mov ax, leng
        cmp ax, 0
        jz goto3
            jmp getchar
        goto3:

        mov ax, 1
        mov minus, ax

        mov dl, '-'
        mov ah, 02h
        int 21h

        mov ax, 1
        mov leng, ax

        jmp getchar
    getchar_stop:

        ret
InputReader ENDP

main:
    mov ax, @data
    mov ds, ax

    mov dx, offset welcomeMessage
    mov ah, 09h
    int 21h

    mov dx, offset GiveMeA
    mov ah, 09h
    int 21h

    CALL InputReader


    mov ax, 4C00h
    int 21h
end main