datarea segment 
mesg1 db 'Please input a number(1,2,3,4,5,,6,7,8) to select style:',13,10 
db '1.small letter to capital letter',13,10 
db '2.capital letter to small letter',13,10 
db '3.bin to hex',13,10 
db '4.hex to bin',13,10 
db '5.dec to bin',13,10 
db '6.bin to dec',13,10 
db '7.hex to dec',13,10 
db '8.dec to hex',13,10,'$' 
mesg2 db 'You have input a invalid number!Please select again:',13,10,'$' 
mesg3 db 'Please input a small letter:',13,10,'$' 
mesg4 db 'Its capital letter is',13,10,'$' 
mesg5 db 'Please input a capital letter:',13,10,'$' 
mesg6 db 'Its small letter is',13,10,'$' 
mesg7 db 'Please input a bin number:',13,10,'$' 
mesg8 db 'Please input a dec number:',13,10,'$' 
mesg9 db 'please input a hex number:',13,10,'$' 
mesg10 db 'Its bin number is',13,10,'$' 
mesg11 db 'Its dec number is',13,10,'$' 
mesg12 db 'Its hex number is',13,10,'$' 
datarea ends 
prognam segment 
main proc far 
assume cs:prognam,ds:datarea 
start: 
push ds 
xor ax,ax 
push ax 
mov ax,datarea 
mov ds,ax 
again: 
lea dx,mesg1 
mov ah,09h 
int 21h 
repeat: 
mov ah,1 
int 21h 
cmp al,31h 
je L1 
cmp al,32h 
je L2 
cmp al,33h 
je L3 
cmp al,34h 
je L4 
cmp al,35h 
je L5 
cmp al,36h 
je L6 
cmp al,37h 
je L7 
cmp al,38h 
je L8 
lea dx,mesg2 
mov ah,9 
int 21h 
jmp repeat 

L1: 
call small_capital 
call crlf 
jmp again 
L2: 
call capital_small 
call crlf 
jmp again 
L3: 
call binhex 
call crlf 
jmp again 
L4: 
call hexbin 
call crlf 
jmp again 
L5: 
call decbin 
call crlf 
jmp again 
L6: 
call bindec 
call crlf 
jmp again 
L7: 
call hexdec 
call crlf 
jmp again 
L8: 
call dechex 
call crlf 
jmp again 
ret 
main endp 

small_capital proc near 
xor ax,ax 
lea dx,mesg3 
mov ah,9 
int 21h 
mov ah,1 
int 21h 
sub al,20h 
push ax 
lea dx,mesg4 
mov ah,9 
int 21h 
pop ax 
mov dl,al 
mov ah,2 
int 21h 
ret 
small_capital endp 

capital_small proc near 
xor ax,ax 
lea dx,mesg5 
mov ah,9 
int 21h 
mov ah,1 
int 21h 
add al,20h 
push ax 
lea dx,mesg6 
mov ah,9 
int 21h 
pop ax 
mov dl,al 
mov ah,2 
int 21h 
ret 
capital_small endp 

binhex proc near 
xor ax,ax 
mov bx,ax 
lea dx,mesg7 
mov ah,9 
int 21h 
mov si,4 
newchar1: 
mov ah,1 
int 21h 
sub al,30h 
jl rotate1 
cmp al,10d 
jl add_to1 
jmp rotate1 

add_to1: ;save bin to bx 
mov cl,1 
shl bx,cl 
mov ah,0 
add bx,ax 
jmp newchar1 
rotate1: 
lea dx,mesg12 
mov ah,9 
int 21h 

rotate1_1: 
mov cl,4 
rol bx,cl 
mov al,bl 
and al,0fh 
add al,30h 
cmp al,3ah 
jl print1 
add al,7h 
print1: 
mov dl,al 
mov ah,2 
int 21h 
dec si 
jnz rotate1_1 
ret 

binhex endp 

hexbin proc near 
mov bx,0 
lea dx,mesg9 
mov ah,9 
int 21h 
mov si,16 
newchar2: 
mov ah,1 
int 21h 
sub al,30h 
jl print2 
cmp al,10d 
jl add_to2 

sub al,27h 
cmp al,0ah 
jl print2 
cmp al,10h 
jge print2 
add_to2: 
mov cl,4 
shl bx,cl 
mov ah,0 
add bx,ax 
jmp newchar2 

lea dx,mesg10 
mov ah,9 
int 21h 
print2: 
rol bx,1 
mov al,bl 
and al,1h 
add al,30h 
mov dl,al 
mov ah,2 
int 21h 
dec si 
jnz print2 
ret 
hexbin endp 

decbin proc near 
lea dx,mesg8 
mov ah,9 
int 21h 

mov bx,0 
newchar3: 
mov ah,1 
int 21h 

sub al,30h 
jl print3 
cmp al,9d 
jg print3 
cbw 

xchg ax,bx 
mov cx ,10d 
mul cx 
xchg ax,bx 
add bx,ax 
jmp newchar3 
print3: 
lea dx,mesg10 
mov ah,9 
int 21h 

rol bx,1 
mov al,bl 
and al,1h 
add al,30h 
mov dl,al 
mov ah,2 
int 21h 
dec si 
jnz print3 

ret 
decbin endp 

bindec proc near 
lea dx,mesg7 
mov ah,9 
int 21h 
newchar4: 
mov ah,1 
int 21h 
sub al,30h 
jl print4 
cmp al,10d 
jl add_to4 
jmp print4 
add_to4: 
mov cl,1 
shl bx,cl 
mov ah,0 
add bx,ax 
jmp newchar4 
print4: 
lea dx,mesg11 
mov ah,9 
int 21h ;display dec 
mov cx,10000d 
call dec_div4 
mov cx,1000 
call dec_div4 
mov cx,100 
call dec_div4 
mov cx,10 
call dec_div4 
mov cx,1 
call dec_div4 
ret 
dec_div4 proc near 
mov ax,bx 
mov dx,0 
div cx 
mov bx,dx 
mov dl,al 
add dl,30h 
mov ah,2 
int 21h 
ret 
dec_div4 endp 

bindec endp 

hexdec proc near 
lea dx,mesg9 
mov ah,9 
int 21h 
mov bx,0 
newchar5: 
mov ah,1 
int 21h 
sub al,30h 
jl next5 
cmp al,10d 
jl add_to5 
sub al,27h 
cmp al,0ah 
jl next5 
cmp al,10h 
jge next5 
add_to5: 
mov cl,4 
shl bx,cl 
mov ah,0 
add bx,ax 
jmp newchar5 
next5: 
lea dx,mesg11 
mov ah,9 
int 21h ;display dec 
mov cx,10000d 
call dec_div5 
mov cx,1000d 
call dec_div5 
mov cx,100d 
call dec_div5 
mov cx,10d 
call dec_div5 
mov cx,1d 
call dec_div5 
ret 
hexdec endp 
dec_div5 proc near 
mov ax,bx 
mov dx,0 
div cx 
mov bx,dx 
mov dl,al 
add dl,30h 
mov ah,2 
int 21h 
ret 
dec_div5 endp 


dechex proc near 
lea dx,mesg11 
mov ah,9 
int 21h 
mov bx,0 
newchar6: 
mov ah,1 
int 21h 
sub al,30h 
jl next6 
cmp al,9d 
jg next6 
cbw 
xchg ax,bx 
mov cx,10d 
mul cx 
xchg ax,bx 
add bx,ax 
jmp newchar6 
next6: 
mov si,4 
lea dx,mesg12 
mov ah,9 
int 21h 
rotate6: 
mov cl,4 
rol bx,cl 
mov al,bl 
and al,0fh 
add al,30h 
cmp al,3ah 
jl print6 
add al,7h 
print6: 
mov dl,al 
mov ah,2 
int 21h 
dec ch 
jnz rotate6 
ret 
dechex endp 
crlf proc near 
mov dl,13 
mov ah,2 
int 21h 
mov dl,10 
mov ah,2 
int 21h 
ret 
crlf endp 
prognam ends 
end start

看以什么方式輸出了。 
要是以十進制形式輸出，要將AX分別除以10000、1000、100、10分離出每一位，分別加上30H存放在字符串里，還要判斷左邊是不是以零開頭，從第一個不是零的位開始輸出； 
要是以十六進制形式輸出就比較簡單，通過移位和邏輯運算分別分離出四組四位二進制，通過查表轉換成相應的數字字符和字母字符輸出就行了