汇编语言：一段英文中各字母的个数

.MODEL SMALL
.DATA
STRING1 DB 'PLEASE ENTER ONE SENTENCE$';
STRING2 DB 'THE RESULT:$';	
num db 53 dup(?)					
.CODE
main proc far
  	mov ax,@data
  	mov ds,ax
  	call init	
  	call read
  	call output		
main endp
init proc near 
	mov cx,53
	mov bx,0
init1:
	mov num[bx],0
	inc bx
loop init1
	ret
init endp
;------------------------------
read proc near
	lea dx,STRING1
  	mov ah,09h
  	int 21h
read2:
 	mov ah,01h
 	int 21h
 	cmp al,0dh
 	je exit 
 	sub al,40h
 	cmp al,1bh
 	jl  read1
 	sub al,5
read1:
	cbw
	mov bx,ax
	inc num[bx]
	jmp read2 	
exit:
    ret
read endp 
;------------------------------
output proc near
	lea dx,STRING2
    mov ah,09h
    int 21h
    mov bx,1
output1:
	inc bx
	cmp bx,53
	je exit
	cmp num[bx],0
	je output1
	cmp bx,27
	jg output2
	mov ax,bx
	add ax,40h
	mov dl,al
	mov ah,02h
	int 21h
	jmp output3	
output2:
	mov ax,bx
	add ax,45h
	mov dl,al
	mov ah,02h
	int 21h
output3:
	mov si,0
	mov al,num[bx]
	cbw
output4:
	mov dx,0
	mov cx,10
	div cx
	add dx,30h
	push dx
	inc si
	cwd
	cmp ax,0
	je output5
	jmp output4
output5:
	pop ax
	dec si
	mov dl,al
	mov ah,02h
	int 21h
	cmp si,0
	jne output5
	mov dl,' '
	mov ah,02h
	int 21h
	jmp output1
exit:
    ret		
output endp  
ENDING:
  MOV AX,4C00H;		终止程序
  INT 21H
END