Question

I am having problem on how exactly should i use loop to get the desire output in this program,

What i want to do is to take input any number from the user and then sort that number in descending order,

I tried my best here to explain every step of the code in the comment.

here is my code,

STSEG SEGMENT
        DB 64 DUP(?)
STSEG ENDS

DTSEG SEGMENT
        SNAME    DB 24 DUP("$")


DTSEG ENDS

CDSEG SEGMENT
    MAIN PROC
    ASSUME CS:CDSEG, DS:DTSEG, SS:STSEG

    MOV AX,DTSEG
    MOV DS,AX
    MOV ES, AX     ;ES:DI


    MOV DX, OFFSET STRNG1
    MOV AH,09
    INT 21H

    XOR DX,DX


      MOV BYTE PTR SNAME, 40
      MOV DX, OFFSET SNAME  

      MOV AH, 0AH
      INT 21H


      PUSH DX ;Hold the input number in a stack until we clear the screen and set the cursor
      ; The clear screen and cursor position code is here which i didn't really mention.

      ;What we need to do now is to compare first number to each other number and store the greatest


 of two on first position.


      MOV BX,DX ;Copy un-sorted number to BX, 

      MOV AX,BX[1] ;the length of the number which is stored on the first position of the string
      XOR AH,AH      ;Empty AH
      MOV CL,AL  ;MOVE AL into CL for looping 6 times
      SUB CL,1

      MOV SI,02H ;the number is stored in string array from the 2nd position


;Suppose the input number is the following,
      ;[6][3][9][1][8][2][6]

      ;this is how it should work,


      ; Loop 6 times , CX = 6
      [7][6][3][9][1][8][2][6] ; 7 is length of the number which is already copied in CX above.
      ; but we need 6 iterations this is why we subtract 1 from CL above.

      ; 6 > 3 ? 
      ; Yes, then BX[SI] = 6 and BX[SI+1] = 3
      ; 6 > 9 ?
      ; NO, then BX[SI] = 9  and BX[SI+2] = 6
      ; 9 > 1   
      ; Yes, then BX[SI] = 9 and BX[SI+3] = 1
      ; 9 > 8
      ; Yes, then BX[SI] = 9 and BX[SI+4] = 8 
      ; 9 > 2
      ; Yes, then BX[SI] = 9 and BX[SI+5] = 2 
      ; 9 > 6
      ; Yes, then BX[SI] = 9 and BX[SI+6] = 6

; After first iteration the incomplete sorted number is,
;[9][3][6][1][8][2][6]

  ;Similarly here i need to loop 5 times now by comparing the 2nd number which is a 3 with all ;the number after it and then loop 4 times then 3 times then two times and then 1 time.


     L1: 
        ;Loop 1 must iterate 6 time for the supposed input number, 
;but i couldn't be able to write the proper code as i always get out of registers. kindly help me out   

        L2:


        LOOP L2


     Loop L1

Kindly help me with the nested loop where i’ve stucked.

Answer 1

The loop instruction uses the cx register.

So you must either preserve cx for the outer loop with e.g. push cx (before L2🙂 and pop cx (after loop L2):

    mov  cx,5
L1:
    push cx
    mov  cx,6
L2:
    . . . do stuff inner
    loop L2
    pop  cx
    . . . do stuff outer 
    loop L1

or remember that loop is roughly equal to dec cx jnz, so do e.g.

    mov  dx,5
L1:
    mov  cx,6
L2:
    ... do stuf inner
    loop L2
    .. do stuff outer
    dec  dx
    jnz  L1

Possible off-by-one errors are intended and meant as an exercise for the reader 🙂