15 replies to this topic

[ipride]

I need help with my assi. I don't even understand what the question is . Q. write a program that will input an integer valve and calculate the value of nBr where nBr is the smallest integer such that 1^2 + 2^2 + 3^2 +....... nBr^2 >= value
( these are square of one and two .....)
for example if you input 50, then the program would display 5 since 1+4+9+16 = 30, but 1+4+9+16+25= 55

[dargueta]

Try writing it out in pseudocode first. How would you do it by hand?

[ipride]

dargueta said:

Try writing it out in pseudocode first. How would you do it by hand?

here is the design I came up with
Value: = 0;
number := 0;
While(value <= number)
Multiply number x number
Add 1 to number
Until (value == number);

does it look ok?

[dargueta]

You're very close:

value = 0;
number = 0;
numbertotal = 0;

while( 1 )
{
    numbertotal += number * number;

    if( numbertotal >= value )
        return number;
    else
        ++number;
}

Next step: assign variables to registers. (I highly discourage using any of the DX, EDX, RDX registers.)

Edited by dargueta, 28 February 2010 - 08:28 PM.
Fixed little mistake.

[ipride]

thank you for all the help here is what my code looks like, please send any comments if you have.

.586

.MODEL FLAT


INCLUDE io.h            ; header file for input/output


.STACK 4096


.DATA

targetValue   DWORD   ?

nbrTerms      DWORD   ?

number        DWORD   ?

prompt1 BYTE    "Enter the integer value", 0

string  BYTE    40 DUP (?)

resultLbl BYTE  "Number of terms", 0

nbrTerms     BYTE    11 DUP (?), 0


.CODE

_MainProc PROC

		input   prompt1, string, 40      ; read ASCII characters

		atod    string                   ; convert to integer

		dtoa    targetValue, ecx         ; convert to ASCII characters

	mov    targetValue,0	 ;value :=0

	mov   ecx,targetValue          ;store targetValue in ecx

	mov   nbrTerms,0                ;number of terms:=0

	mov  eax,nbrTerms	              ;store nbrTerms in eax

	mov     number,0		 ;number:=0

	mov	ah,number	 ;store number in ah

        

whileB:    cmp     nbrTerms,1	;nbrTerms==1

	jne     endwhileB	             ;exit if not equal

			

	add   ah,ah		;multiply number by itself

ifB:	cmp  ecx,eax		;comparing targetVale to nbrTerms

	jnle   ifB	                          ;exit if not targetVale<= nbrTerms		inc    eax		             ;add 1 increment++

	jmp     whileB		 ;repeat the while loop

			

endloop:          

	output  resultLbl, nbrTerms          ; output labeLb1 nbrTerms


	mov     eax, 0                            ; exit with return code 0

	ret

_MainProc ENDP

END                                                     ; end of source code

[dargueta]

Quote

add ah,ah ;multiply number by itself

This is wrong. You want x^2, not x*2. You need to use the MUL instruction.

Quote

mov eax, 0 ; exit with return code 0

Use XOR EAX, EAX instead. Reduces code size and executes faster.

Instead of putting variables in memory, try to use registers if you can.

Also:
1) Since you never assign to nbrTerms after you declare it, it's going to go into an infinite loop.
2) There's no endWhileB label.
3) Why are you assigning 0 to a memory variable, assigning that to a register, and then using the registers?
4) You never write your results back to memory before outputting them. You're going to get unexpected results.

[ipride]

dargueta said:

This is wrong. You want x^2, not x*2. You need to use the MUL instruction.


Use XOR EAX, EAX instead. Reduces code size and executes faster.

Instead of putting variables in memory, try to use registers if you can.

Also:
1) Since you never assign to nbrTerms after you declare it, it's going to go into an infinite loop.
2) There's no endWhileB label.
3) Why are you assigning 0 to a memory variable, assigning that to a register, and then using the registers?
4) You never write your results back to memory before outputting them. You're going to get unexpected results.

******************************************************************************************************************************************************************************
Ok I’m a little confused now,
1)Since you never assign to nbrTerms after you declare it, it's going to go into an infinite loop.

Does that mean I don’t have to declare it at all?
2. I assigned 0 to memory because I thought that we have to initialize targetValue to zero , same with nbrTerms = 0 that means I don’t have to add the lines
mov targetValue,0
mov nbrTerms,0
this part I didn’t get it
4) You never write your results back to memory before outputting them. You're going to get unexpected results

[dargueta]

Ok, I'll explain:

1) You only have to declare it if output cannot take a register as its second argument. Otherwise it's useless, as are targetValue and number, as well as the first nbrTerms you declared. (I just noticed you declared it twice.)

2) If you push these variables into registers you won't have to use memory. Memory is slooow. Take my word for it.
4)

    input   prompt1, string, 40     ; read ASCII characters
    ...
[COLOR="GREEN"]    mov     nbrTerms,0              ;number of terms:=0[/COLOR]
    ...

whileB:
[COLOR="RED"]    cmp     nbrTerms,1              ;nbrTerms==1
    jne     endwhileB               ;exit if not equal
[/COLOR]
    add     ah,ah                   ;multiply number by itself
ifB:
    cmp     ecx,eax                 ;comparing targetVale to nbrTerms
    jnle    ifB                     ;exit if not targetVale<= nbrTerms
    inc     eax                     ;add 1 increment++
    jmp     whileB                  ;repeat the while loop

endloop:
[COLOR="BLUE"]    output  resultLbl, nbrTerms     ; output labeLb1 nbrTerms[/COLOR]
    mov     eax, 0                  ; exit with return code 0
    ret

Notice that you assign nbrTerms to 0 (green) and then never assign it again. This means that it will always be 0, and the exit condition for your loop (red) will never execute. So you'll never exit your loop. Even if by magic you break out of the loop, your output (blue) will always be 0.

[ipride]

thank you again I made some changes to the code but I'm still running to errors.

.586

.MODEL FLAT


INCLUDE io.h            ; header file for input/output


.STACK 4096


.DATA

targetValue   DWORD   ?

nbrTerms      DWORD   ?

number        DWORD   ?

prompt1 BYTE    "Enter the integer value", 0

string  BYTE    40 DUP (?)

resultLbl BYTE  "Number of terms", 0

nbrTerms     BYTE    11 DUP (?), 0


.CODE

_MainProc PROC

	input   prompt1, string, 40      ; read ASCII characters

	atod    string                        ; convert to integer

	dtoa    targetValue, ecx         ; convert to ASCII characters

	mov     ecx,targetValue	   ;store targetValue in ecx

	mov     eax,nbrTerms	   ;store nbrTerms in eax

	mov	ah,number	  ;store number in ah 

        

whileB:     cmp     nbrTerms,1	  ;nbrTerms==1

	  jne     endwhileB		  ;exit if not equal

			

	 mul	ah,ah		  ;multiply number by itself

ifB:	cmp	ecx,eax		  ;comparing targetVale to nbrTerms

	jnle	ifB		  ;exit if not targetVale<= nbrTerms

	inc  eax			  ;add 1 increment++

	jmp     whileB		  ;repeat the while loop

			

endwhilB:          

	output  resultLbl, nbrTerms          ; output labeLb1 nbrTerms


	mov     eax,eax  ; exit 

	ret

_MainProc ENDP

END                             ; end of source code

[dargueta]

A few problems you need to fix:

     mul    ah,ah                   ;multiply number by itself

Illegal. MUL only takes one operand, the accumulator (AL, AX, EAX) is the other operand you're multiplying by. Allow me to demonstrate:

mul    cl
; al * cl, ax contains result

mul    cx
; ax * cx, dx:ax contains result

mul    ecx
; eax * ecx, edx:eax contains result

This is why I hinted earlier that you shouldn't use any of the *DX registers.

    mov     eax,eax  ; exit 

You need to change this to XOR EAX, EAX.

    mov     ecx,targetValue         ;store targetValue in ecx
    mov     eax,nbrTerms            ;store nbrTerms in eax
    mov     ah,number               ;store number in ah 

If these comments are correct, you've got the operands flipped. You need MOV number, AH and so on. Either that or the operands are in the right order but your comments are wrong.
Plus, you're storing nbrTerms into EAX, and then storing number into AH. AH is part of EAX, so you're overwriting your own data. You need to use a different register.

And you still have the "never writing to nbrTerms" error.

[ipride]

this is harder than what thought thank you for all the help I'm not sure why they assigning a problem like this if it's only intro to asseembly. I made some change to assigning registers.

.586

.MODEL FLAT


INCLUDE io.h            ; header file for input/output


.STACK 4096


.DATA

targetValue   DWORD   ?

number        DWORD   ?

prompt1 BYTE    "Enter the integer value", 0

string  BYTE    40 DUP (?)

resultLbl BYTE  "Number of terms", 0

nbrTerms     BYTE    11 DUP (?), 0


.CODE

_MainProc PROC

	input   prompt1, string, 40      ; read ASCII characters

	atod    string                        ; convert to integer

	dtoa    targetValue, cl            ; convert to ASCII characters

	mov   cl,targetValue	   ;store targetValue in cl

	mov   cx,nbrTerms		   ;store nbrTerms in cx

	mov   number,ah		   ;store number in ah

        

whileB:     cmp     nbrTerms,1	   ;nbrTerms==1

	jne     endwhileB		   ;exit if not equal

			

	mul  cl   			   ;multiply number by itself

ifB:	cmp	cl,cx		   ;comparing targetVale to nbrTerms

	jnle	ifB		   ;exit if not targetVale<= nbrTerms

	inc	ah		   ;add 1 increment++

	jmp     whileB		   ;repeat the while loop

			

endwhilB:          

	output  resultLbl, nbrTerms          ; output labeLb1 nbrTerms


	xor    eax,eax  ; exit 

	ret

_MainProc ENDP

END                             ; end of source code

[dargueta]

mov   cl,targetValue	   ;store targetValue in cl
mov   cx,nbrTerms		   ;store nbrTerms in cx

Two things wrong with this:
1) targetValue and nbrTerms are declared as DWORDs. This means you must use one of the 32-bit registers, e.g. EAX, EBX, ECX, etc. to hold them.
2) You're doing the same thing again with CL/CX - overwriting your own data.

You also misspelled endwhileB in your exit label.