CODEWITHSUNDEEP
loopsif-statementassemblyemu8086
000
000

Reputation: 405

write a loop to print 0 to 99 in decrement order (assembly)

I am new in assembly , I am using emu8086 question : user will input a number between 99 to 0 , let it is 88 i have to print 88 to zero .

to do this , i was trying this technique :

  1. call AH,1 two times for MSB and LSB

  2. copy MSB TO BH and LSB to BL

  3. for each bh

    ->check if bh is 0

    ->true,then check bl trough update_it if it is 0

        ->true,then goto exit (because number is 00)

    ->false,then decrement msb and add 9 to lsb ( make 80 to 79 ) 
      and goto loop 2 to print it

    ->false then do normal lsb decrement ( 77 to 76 )

but i always get the wrong output combining many characters , please mention my mistake . thanks in advance .

here is my code

.MODEL SMALL

.STACK 100H  

.DATA 

.CODE 
MAIN PROC

;INITIALIZE DS
MOV AX,@DATA
MOV DS,AX

MOV AH,1         ;SCAN MSB
INT 21H          ;MSB IS NOW AT AH
MOV BH,AL        ;SAVE IT TO BH

                 ;SCAN LSB
MOV AH,1         ;LSB IS NOW AT AL
INT 21H          ;SAVE IT TO BL
MOV BL,AL  

MOV AH,2         ;SINGLE CHAR PRINT
MOV DL,0DH       ;CARRIAGE RETURN
INT 21H          ;AL = 0DH

MOV DL,0AH       ;LINE FEED
INT 21H          ;AL = 0AH

;PRINT THE FIRST NUMBER

MOV DL,BH        ;MSB
INT 21H          ;

MOV DL,BL        ;LSB
INT 21H          ;



LOOP1:

    CMP BL,0       ;LET 70 
                   ;SO UPDATE O TO 9
                   ;AND 7 TO 6
    JE  UPDATE_IT  ;IF TRUE

    JMP LOOP2      ;IF FASLE


LOOP2:


    MOV DL,' '     ;SPACE
    INT 21H

    MOV DL,BH      ;MSB
    INT 21H

    MOV DL,BL      ;LSB
    INT 21H 


    DEC BL         ;DECREMENT LSB


    JMP LOOP1 

UPDATE_IT:

    CMP BH,0       ;BOTH MSB 
                   ;AND LSB ARE ZERO
    JE  EXIT_      ;IF TRUE EXIT = 00


    DEC BH         ;IF FALSE 
                   ;DEC MSB
    ADD BL,9       ;TURN LSB O TO 9
                   ;EXAMPLE 80 TO 79
    JMP LOOP2      ;DO NORMAL DECREMENT

;DOS EXIT                    
EXIT_:             
MOV AH,4CH         ;DOS EXIT FUNCTION
INT 21H            ;EXECUTE

MAIN ENDP

END MAIN

Upvotes: 2

Views: 1818

Answers (1)

Tommylee2k
Tommylee2k

Reputation: 2731

your approach nearly worked, the main problem was: you've mistaken 0 with ascii '0' (0x30)
Your loop should end when '0' was reached (to be more precise: you also want to print '10','20','30' etc... so the loop has to stop when '0' was PASSED, not reached. therefore the -1 in cmp '0'-1)

( I also allowed myself to move the outer loop to UNDER the loop body, to remove the need of the initial output of the first number )

.MODEL SMALL
.STACK 100H  
.DATA 

.CODE 
MAIN PROC

;INITIALIZE DS
MOV AX,@DATA     ; not sure this is really needed in model .small
MOV DS,AX

MOV AH,1         ;SCAN MSB
INT 21H          ;MSB IS NOW AT AH
MOV BH,AL        ;SAVE IT TO BH

                 ;SCAN LSB
MOV AH,1         ;LSB IS NOW AT AL
INT 21H          ;SAVE IT TO BL
MOV BL,AL  

MOV AH,2         ;SINGLE CHAR PRINT
MOV DL,0DH       ;CARRIAGE RETURN
INT 21H          ;AL = 0DH
MOV DL,0AH       ;LINE FEED
INT 21H          ;AL = 0AH

LOOP1:
    MOV DL,' '     ;SPACE
    INT 21H
    MOV DL,BH      ;MSB
    INT 21H
    MOV DL,BL      ;LSB
    INT 21H 

    DEC BL         ;DECREMENT LSB
    CMP BL,'0'-1   ;LET 70 
                   ;SO UPDATE O TO 9
                   ;AND 7 TO 6
    JNE LOOP1      ;IF FALSE

UPDATE_IT:         ; IF LST was zero

    MOV BL,'9'     ;TURN LSB O TO 9
                   ;EXAMPLE 80 TO 79

    DEC BH
    CMP BH,'0'-1   ;BOTH MSB 
                   ;AND LSB ARE ZERO
    JNE LOOP1      

;DOS EXIT                    
EXIT_:             
MOV AH,4CH         ;DOS EXIT FUNCTION
INT 21H            ;EXECUTE

MAIN ENDP
END MAIN

Upvotes: 4

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