DOS功能调用，看看

DATA SEGMENT 
INPUT   DB 10
 DB ?
 DB 10 DUP(?)
 DB '$' 
MSG1 DB 'Want input(Y/N):',0DH,0AH,'$' 
HEADMSG DB 0DH,0AH,'please input a string:',0DH,0AH,'$'
MSG2 DB 0DH,0AH,'your inputting is:',0DH,0AH,'$' 
MSG3 DB 0DH,0AH,'Want continue(Y/N)?','$'
MSG4 DB 0DH,0AH,'$'
DATA ENDS

CODE SEGMENT
ASSUME CS:CODE,DS:DATA
START: 
 MOV AX,DATA
 MOV DS,AX
STEP1: MOV AH,9
 MOV DX,OFFSET MSG1
 INT 21H
 MOV AH,1
 INT 21H
 CMP AL,'Y'
 JE STEP2
 CMP AL,'N'
 JE EXIT
 JMP STEP1
STEP2: MOV AH,9
 MOV DX,OFFSET HEADMSG
 INT 21H