使用x86汇编语言编写输入年、月、日，判断当日的星期数，并进行输出的代码。该代码使用Intel语法，需要在DOSBox或类似的环境中运行。

好的，以下是代码：

.model small
.stack 100h

.data
; 定义一些常量
year db ?
month db ?
day db ?
dayOfWeek db ?
prompt1 db 'Please enter year (yyyy): $'
prompt2 db 'Please enter month (mm): $'
prompt3 db 'Please enter day (dd): $'
output db 'The day of the week is: $'
sunday db 'Sunday', 13, 10, '$'
monday db 'Monday', 13, 10, '$'
tuesday db 'Tuesday', 13, 10, '$'
wednesday db 'Wednesday', 13, 10, '$'
thursday db 'Thursday', 13, 10, '$'
friday db 'Friday', 13, 10, '$'
saturday db 'Saturday', 13, 10, '$'

.code
main proc
    mov ax, @data
    mov ds, ax

    ; 依次获取用户输入的年、月、日
    lea dx, prompt1
    mov ah, 9
    int 21h
    mov ah, 1
    int 21h
    sub al, 48 ; 将字符转换成数字
    mov year, al

    lea dx, prompt2
    mov ah, 9
    int 21h
    mov ah, 1
    int 21h
    sub al, 48
    mov month, al

    lea dx, prompt3
    mov ah, 9
    int 21h
    mov ah, 1
    int 21h
    sub al, 48
    mov day, al

    ; 根据公式计算当日的星期数
    mov ah, 0
    mov al, year
    mov bl, 4
    div bl ; year / 4
    add ax, year ; year / 4 + year
    add ax, day ; year / 4 + year + day
    mov bl, month
    sub bl, 1
    mov cl, 2
    mul cl ; (year / 4 + year + day) * 2
    add ax, bl ; (year / 4 + year + day) * 2 + month - 1
    cmp bl, 2
    jne notFeb
    dec ax ; 二月份要减一
notFeb:
    mov bl, 12
    mul bl ; (year / 4 + year + day) * 2 + month - 1 + 13 * (month + 1) / 5
    mov cl, 13
    add bl, cl
    mov cl, 5
    div cl
    add ax, bl
    add ax, 6 ; (year / 4 + year + day) * 2 + month - 1 + 13 * (month + 1) / 5 + 6
    and ax, 7 ; 取余数
    mov dayOfWeek, al

    ; 输出结果
    lea dx, output
    mov ah, 9
    int 21h
    cmp dayOfWeek, 0
    je sundayLabel
    cmp dayOfWeek, 1
    je mondayLabel
    cmp dayOfWeek, 2
    je tuesdayLabel
    cmp dayOfWeek, 3
    je wednesdayLabel
    cmp dayOfWeek, 4
    je thursdayLabel
    cmp dayOfWeek, 5
    je fridayLabel
    cmp dayOfWeek, 6
    je saturdayLabel
sundayLabel:
    lea dx, sunday
    jmp printLabel
mondayLabel:
    lea dx, monday
    jmp printLabel
tuesdayLabel:
    lea dx, tuesday
    jmp printLabel
wednesdayLabel:
    lea dx, wednesday
    jmp printLabel
thursdayLabel:
    lea dx, thursday
    jmp printLabel
fridayLabel:
    lea dx, friday
    jmp printLabel
saturdayLabel:
    lea dx, saturday
printLabel:
    mov ah, 9
    int 21h

    mov ah, 4ch
    int 21h
main endp
end main

代码中的注释已经说明了每个步骤的含义。请在类 DOSBox 的环境中运行该代码。