Print text in assembly-CodePudding

I am new in assembly and I had my first lesson few days ago.
I got an assignment to add my name to a program that prints "Hello,world!" and I successfully did that, but I have a strange space between the "Hello,world!" and my name.
Can someone tell me how I can fix that and why does it happen?

Here is my code:

name "hi-world"

; this example prints out  "hello world!"
; by writing directly to video memory.
; in vga memory: first byte is ascii character, byte that follows is character attribute.
; if you change the second byte, you can change the color of
; the character even after it is printed.
; character attribute is 8 bit value,
; high 4 bits set background color and low 4 bits set foreground color.

; hex    bin        color
; 
; 0      0000      black
; 1      0001      blue
; 2      0010      green
; 3      0011      cyan
; 4      0100      red
; 5      0101      magenta
; 6      0110      brown
; 7      0111      light gray
; 8      1000      dark gray
; 9      1001      light blue
; a      1010      light green
; b      1011      light cyan
; c      1100      light red
; d      1101      light magenta
; e      1110      yellow
; f      1111      white

org 100h

; set video mode    
mov ax, 3     ; text mode 80x25, 16 colors, 8 pages (ah=0, al=3)
int 10h       ; do it!

; cancel blinking and enable all 16 colors:
mov ax, 1003h
mov bx, 0
int 10h

; set segment register:
mov     ax, 0b800h
mov     ds, ax

; print "hello world"
; first byte is ascii code, second byte is color code.

mov [02h], 'H'

mov [04h], 'e'

mov [06h], 'l'

mov [08h], 'l'

mov [0ah], 'o'

mov [0ch], ','

mov [0eh], 'W'
 
mov [10h], 'o'

mov [12h], 'r'

mov [14h], 'l'

mov [16h], 'd'

mov [18h], '!'

mov [20h], 't'

mov [22h], 'e'

mov [24h], 's'

mov [26h], 't'
     


; color all characters:
mov cx, 12  ; number of characters.
mov di, 03h ; start from byte after 'h'

c:  mov [di], 11101100b   ; light red(1100) on yellow(1110)
    add di, 2 ; skip over next ascii code in vga memory.
    loop c

; wait for any key press:
mov ah, 0
int 16h

ret

And this is the result:

CodePudding user response：

mov [02h], 'H'
mov [04h], 'e'
mov [06h], 'l'
mov [08h], 'l'
mov [0ah], 'o'
mov [0ch], ','
mov [0eh], 'W'
mov [10h], 'o'
mov [12h], 'r'
mov [14h], 'l'
mov [16h], 'd'
mov [18h], '!'

The offset addresses that are being used in these instructions are expressed in the hexadecimal number representation and are being incremented by 2.
Looking at

mov [08h], 'l'
mov [0ah], 'o'

we see that the next word after 08h is not at 10h but rather at 0Ah. Hexadecimal uses the digits {0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F}. Therefore incrementing 8 by 2 will produce A.
If you want your additional text to follow immediately behind the exclamation mark, then a similar change has to be taken after:

mov [18h], '!'

What you did

00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
      ^     ^     ^     ^     ^     ^     ^
      H     e     l     l     o     ,     W

10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F
^     ^     ^     ^     ^
o     r     l     d     !                 <-- the 3-character gap that you see

20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F
^     ^     ^     ^
t     e     s     t

What you need

00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
      ^     ^     ^     ^     ^     ^     ^
      H     e     l     l     o     ,     W

10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F
^     ^     ^     ^     ^
o     r     l     d     !     r     o     e

20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F

e