assembly - Strange output with Irvine's WriteString -

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the point of following program print out letter "c" combination of every background , foreground color.

in library i'm using colors defined 0-15 , following code: 

mov eax,foreground + (background * 16)  call settextcolor

here code: 

include irvine32.inc .data  character byte "c" count dword ? background dword 0  .code main proc     call clrscr      mov ecx, 15                             ; our main counter 0-15 colors  l1:          mov count, ecx                          ; store our outer loop counter     mov ecx, 15                             ; set out inner loop counter l2:          ; since our color defined so... mov eax,foreground + (background * 16)     mov eax, count                          ; setup our foreground color     add eax, background                     ; setup our background color     call settextcolor      ;  instead of multiplying each background color 16, going      ; add 16 each time.      add background, 16                            ; print character     mov edx, offset character     call writestring      loop l2      mov ecx, count                          ; reset our outside loop     loop l1      call crlf     exit main endp  end main

now, i'm using windows 7, above code "works" reason, goes point, program stops, , computer starts beeping. also, @ point in program, starts printing random characters letter c.. here output: 

c♀c♀c♀c♀c♀c♀c♀c♀c♀c♀c♀c♀c♀c♀c♀c♂c♂c♂c♂c♂c♂c♂c♂c♂c♂c♂c♂c♂c♂c♂c c c c c c c c c c c c c c c c       c       c       c       c       c       c       c       c       c c       c       c       c       c       cccccccccccccccc♠c♠c♠c♠c♠c♠c♠c♠c♠c♠c♠c♠c ♠c♠c♠c♣c♣c♣c♣c♣c♣c♣c♣c♣c♣c♣c♣c♣c♣c♣c♦c♦c♦c♦c♦c♦c♦c♦c♦c♦c♦c♦c♦c♦c♦c♥c♥c♥c♥c♥c♥c♥c ♥c♥c♥c♥c♥c♥c♥c♥c☻c☻c☻c☻c☻c☻c☻c☻c☻c☻c☻c☻c☻c☻c☻c☺c☺c☺c☺c☺c☺c☺c☺c☺c☺c☺c☺c☺c☺c☺ press key continue . . .

can tell me why happening?

irvine's writestring needs "null-terminated string". can download chm-file here (irvinelibhelp.exe).

it's little bit sloppy "edx = points string". edx points memory address identifiable label (here: "character"). writestring byte byte location , write character or control directive regardless of real type or intention until comes across byte value 0. masm has no directive define string last 0, has added manually:

character byte "c", 0

an alternative way print character use writechar:

... ; print character mov al, character call writechar loop l2  mov ecx, count                          ; reset our outside loop loop l1 ...

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