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assemblyx86-16emu8086

inc instruction changes next one value in an array

I declare this array:

array dw 10 dup(0)

But when I want to increase a value with this:

mov bx, 5
inc array[bx]

It changes next one by 256 and the correct value by 1: Like this

enter image description here

Solution

  • Your array initializes these 20 bytes in memory:

    0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0

    The instructions

    mov bx, 5
inc array[bx]

    will change the array to

    0,0,0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0

    because BX is used as an offset measured in bytes from the start of the array.

    The screenshot that you've posted is easily created from trying to visualize the word-sized elements from the array but incrementing by 1 the pointer that is used in the algorithm instead of raising that pointer by 2 which would be correct.

    0,0                         0:
  0,0                       0:
    0,0                     0:
      0,0                   0:
        0,1               256: 
          1,0               1:
            0,0             0:
              0,0           0:
                0,0         0:
                  0,0       0:
                    0,0     0:

    Verify if this is the case...