2.4 Storage of a numeric value with more digits

;Write a program that ask the user a positive integer (possibly composed by more digits, and concluded with ENTER) and saves it into a word variable. The insert of huge values must report an error
;-Deepening: Acquire 5 positive integers separated by ENTER and store them into a word vector

;IMPLEMENTATION
;Use an algorithm in two phases:
;-In first obtain ASCII characters
;-In second, they are converted in integer, evaluating possible presence of overflow

;The two phases can be developed into same cycle

;NB: input from keyboard takes only one number at a time. In this ex I try to store a number with more digits into a variable

.MODEL small
.STACK
.DATA
VAR DW ?
DIM DW ?
STR DW 'Overflow Error'
.CODE
.START

MOV DI,0
MOV CX,10
ciclo: MOV AH,1
       INT 21h
       CMP AL,13; ASCII code of ENTER
       JE cycle0 ; If AL=ENTER, JE does to jump it to cycle0. I do to jump there, so it stores dimension in DIM, otherwise it doesn't
       SUB AL,'0' ; So it prints ASCII character of inserted number
       MOV AH,0
       PUSH AX   ;I store into stack the values taken from keyboard
       INC DI
       CMP DI,5
       JNE ciclo

cycle0:
MOV DIM,DI   ;I must use DIM because if I have a number with less than 5 digits, it gives me problems

cycle1: CMP DI,0   ;DI initially will be = DIM. But when I arrive to 0, it means that I finished
        JE esci
        DEC DI
        MOV BX,DIM ;Here I do BX=DIM-1-DI, i.e., since DI starts from DIM, BX initially will be 0 and slowly grows
        DEC BX
        SUB BX,DI
        POP AX   ;I take last value stored into stack and put it into AX



cycle2: CMP BX,0  ;Descr to below below
        JE aggiungi
        DEC BX
        MUL CX
        JO esciERR ;Overflow da 70000 (su 16bit)
        JMP cycle2


aggiungi: ADD VAR,AX
          JC esciERR ;Overflow da 65535 a 69999
          JMP cycle1

 ;Here there is the error handling
 MOV SI,0
 esciERR:
 MOV AH,2
 MOV DX,STR[SI]
 INT 21h
 INC SI
 CMP SI,15
 JNE esciERR
 esci:
.EXIT
END

;The strategy of code is:
;In ciclo I store numbers entered from keyboard
;somewhere, into a vector or into stack
;like I did.
;In cycle1 what is BX?
;Let's suppose to have read from keyboard 12345:
;Since keyboard reads a digits at the time
;I stored all into stack
;I think my number 12345 as separated in
;units(5),tens(4),hundreds(3) etc...
;So that I can store a number with more digits
;into a variable, first of all BX will be carried to 1, then through MUL CX I multiply
; tens for 10, so 4*10 (BX meanwhile will be decremented to 0), and I sum this to units(5)
;so I have 45. Then, about hundreds, BX will be carried to 2, so everytime that I decrease BX,
;I will have a MUL CX, so, since BX must go down to 0, BX will be decremented 2 times,
;so the digit stored into AL (that is 3) will be multiplied 2 times for 10,
;so I get 300, that will be added at value that is in VAR, that is 45, and I get 345.
;And so on for the remaining digits