Q. Example of Input a Single Digit?

Input a Single Digit for example (0,1, 2, 3, 4, 5, 6, 7, 8, 9)

 CODE SEGMENT

  ...

; Read a single digit in BL register with echo. No error check in the Program 

  MOV AH,  01H

                         INT 21H

; Assuming that the value entered is digit, then its ASCII will be stored in AL. 

; Suppose the key pressed is 1 then ASCII '31' is stored in the AL. To get the 

; Digit 1 in AL subtract the ASCII value '0' from the AL register.

; Here it store 0 as ASCII 30, 

; 1 as 31, 2 as 32.......9 as 39

; To store 1 in memory subtract 30 to get 31 - 30 = 1  

MOV BL, AL

SUB   BL, '0'; '0' is digit 0 ASCII

           ; OR

SUB BL, 30H

; Now BL contain the single digit 0 to 9

; The only code missing here is to check whether the input is in the specific

; Range.

...

CODE ENDS.