I'm developing an Assembly program using the Irvine32 library to print Pascal's Triangle based on user input (ranging from 1 to 13 rows). While the program correctly displays the first few rows, starting from Row 5 onwards, the output becomes garbled and doesn't display the binomial coefficients as intended.
; ---------------------------------------------------------------------------------
; Name: Pascal's Triangulator Program
;
; Description:
; This program prompts the user to enter the number of rows (1-13) they wish to
; print of Pascal's Triangle. It calculates and displays each row with numbers
; separated by spaces. The program includes input validation to ensure the number
; of rows entered is within the specified range.
;
; ---------------------------------------------------------------------------------
INCLUDE Irvine32.inc
; --------------------------------
; Constants
; --------------------------------
MAX_ROWS EQU 13
MIN_ROWS EQU 1
; --------------------------------
; Data Segment
; --------------------------------
.data
; Program Messages
introMsg BYTE "Pascal's Triangulator - Programmed by Cameron Brooks!", 0
introDesc BYTE "This program will print up to 13 rows of Pascal's Triangle, per your specification!", 0
promptMsg BYTE "Enter total number of rows to print [1...13]: ", 0
farewellMsg BYTE "Thank you for using Pascal's Triangulator. Goodbye!", 0
invalidInputMsg BYTE "Invalid input. Please enter a number between 1 and 13.", 0
; Row Formatting
currentRowMsg BYTE "Row ", 0
rowNumberMsg BYTE ": ", 0
; Variables
userRows DWORD ? ; Stores user input
currentRow DWORD ? ; Stores current row index
kValue DWORD ?
binCoeff DWORD ?
.code
main PROC
; Introduction
CALL Introduction
; Prompt user for input
MOV EDX, OFFSET promptMsg
CALL WriteString
; Read integer input
CALL ReadInt
MOV [userRows], EAX ; Store input in userRows
; Validate input (1 <= userRows <= 13)
CMP EAX, MIN_ROWS
JL InvalidInput
CMP EAX, MAX_ROWS
JG InvalidInput
; Initialize loop counter in EBX
MOV EBX, 0 ; EBX = loop counter (starts at 0)
RowLoop:
; Compare loop counter with userRows
CMP EBX, [userRows]
JGE EndProgram ; Exit loop if all rows are printed
; Print "Row X: "
MOV EDX, OFFSET currentRowMsg
CALL WriteString ; Print "Row "
; Print row number (EBX)
PUSH EAX ; Preserve EAX
MOV EAX, EBX ; Load currentRow into EAX
CALL WriteDec ; Print row number
POP EAX ; Restore EAX
; Print ": "
MOV EDX, OFFSET rowNumberMsg
CALL WriteString ; Print ": "
; Set currentRow to EBX
MOV [currentRow], EBX ; Update currentRow
; Print the current row
CALL PrintPascalRow ; Print the current row
; Print newline
CALL CrLf
; Increment loop counter
INC EBX ; EBX++
; Jump back to loop
JMP RowLoop ; Repeat the loop
InvalidInput:
; Handle invalid input
MOV EDX, OFFSET invalidInputMsg
CALL WriteString
CALL CrLf
JMP EndProgram
EndProgram:
; Farewell message
MOV EDX, OFFSET farewellMsg
CALL WriteString
CALL CrLf
; Exit program
EXIT
main ENDP
; ---------------------------------------------------------------------------------
; Procedure: Introduction
; Description:
; Displays the program title and a brief description.
;
; Registers Modified:
; - EAX, EDX
; ---------------------------------------------------------------------------------
Introduction PROC
; Display Introduction Message
MOV EDX, OFFSET introMsg
CALL WriteString
CALL CrLf
; Display Introduction Description
MOV EDX, OFFSET introDesc
CALL WriteString
CALL CrLf
CALL CrLf
RET
Introduction ENDP
; ---------------------------------------------------------------------------------
; Procedure: PrintPascalRow
; Description:
; Prints all binomial coefficients for the current row in Pascal's Triangle.
;
; Registers Modified:
; - EAX, EBX, ESI, EDI, EDX
; ---------------------------------------------------------------------------------
PrintPascalRow PROC
; Preserve EAX, EDX, ESI, and EDI to avoid disrupting the main loop
PUSH EAX ; Preserve EAX
PUSH EDX ; Preserve EDX
PUSH ESI ; Preserve ESI
PUSH EDI ; Preserve EDI
MOV ESI, 0 ; Initialize k to 0
RowElementLoop:
MOV EBX, [currentRow] ; EBX = n (current row index)
CMP ESI, EBX
JG EndRow ; If k > n, end row
; Set kValue
MOV [kValue], ESI ; k = current element index
CALL nChooseK ; binCoeff = nCk
; Print Binomial Coefficient
MOV EAX, [binCoeff] ; Load bin_coeff into EAX
CALL WriteDec ; Print bin_coeff
; Print Space
MOV DL, 32 ; ASCII space character (decimal 32)
CALL WriteChar ; Print space
; Increment k
INC ESI ; k++
; Loop back to print next element
JMP RowElementLoop
EndRow:
; Restore preserved registers
POP EDI ; Restore EDI
POP ESI ; Restore ESI
POP EDX ; Restore EDX
POP EAX ; Restore EAX
RET
PrintPascalRow ENDP
; ---------------------------------------------------------------------------------
; Procedure: nChooseK
; Description:
; Calculates the binomial coefficient "n Choose k" using the multiplicative formula.
;
; Parameters:
; - n is stored in 'currentRow'.
; - k is stored in 'kValue'.
;
; Preconditions:
; - 'currentRow' and 'kValue' contain valid integers where 0 <= k <= n.
;
; Postconditions:
; - 'binCoeff' contains the value of "n Choose k".
;
; Registers Modified:
; - EAX, EBX, ECX, EDX, ESI, EDI, EFLAGS
; ---------------------------------------------------------------------------------
nChooseK PROC
; Save Callee-Saved Registers
PUSH EBX
PUSH ESI
PUSH EDI
; Retrieve n and k
MOV EAX, [currentRow] ; EAX = n
MOV EBX, [kValue] ; EBX = k
; Handle k = 0 or k = n
CMP EBX, 0
JE SetOne
CMP EBX, EAX
JE SetOne
; If k > n, set binCoeff to 0
CMP EBX, EAX
JG SetZero
; Calculate nCk using Multiplicative Formula
MOV ECX, 1 ; Initialize counter i=1
MOV EAX, 1 ; Initialize binCoeff=1
CalcLoop:
CMP ECX, EBX
JG StoreResult
; Calculate (n - i + 1)
MOV ESI, [currentRow] ; ESI = n
SUB ESI, ECX ; ESI = n - i
ADD ESI, 1 ; ESI = n - i + 1
; Multiply binCoeff by (n - i + 1)
MUL ESI ; EAX = EAX * (n - i +1)
; Divide binCoeff by i
MOV EDI, ECX ; EDI = i
XOR EDX, EDX ; Clear EDX for DIV
DIV EDI ; EAX = EAX / i
; Increment i
INC ECX ; i++
JMP CalcLoop
StoreResult:
MOV [binCoeff], EAX ; Store the result
JMP EndCalculation
SetOne:
MOV [binCoeff], 1 ; binCoeff =1
JMP EndCalculation
SetZero:
XOR EAX, EAX ; EAX =0
MOV [binCoeff], EAX ; binCoeff=0
EndCalculation:
; Restore Callee-Saved Registers
POP EDI
POP ESI
POP EBX
RET
nChooseK ENDP
END main
Expected Behavior:
When I input a number between 1 and 5, the program correctly displays the corresponding rows of Pascal's Triangle with proper spacing. For example, entering 4 produces:
Row 1: 11
Row 2: 121
Row 3: 1331
Row 4: 14641
Thank you for using Pascal's Triangulator. Goodbye!
Actual Behavior:
However, when I enter a number greater than 4 (e.g., 5 or 13), the output becomes garbled, for example 13 results in:
Row 1: 11
Row 2: 121
Row 3: 1331
Row 4: 14641
Row 5: 1510
10
51
Row 6: 1615201561
Row 7: 172135#35#2171
Row 8: 12856870F568281
Row 9: 19 36$84T126~126~84T36$9 1
Row 10: 110
45-120x210╥252ⁿ210╥120x45-10
1
Row 11: 111
557165Ñ330J462╬462╬330J165Ñ55711
1
Row 12: 112
66B220▄495∩792924£792495∩220▄66B12
1
Thank you for using Pascal's Triangulator. Goodbye!
Problem Details:
Rows 0-4: Correctly display the first six rows without proper spacing.
Rows 5-13:
What I've Tried:
Questions:
Additional Information:
Assembler and Environment: Using MASM with the Irvine32 library in a 32-bit Windows environment.
Previous Attempts: Followed previous suggestions to preserve additional registers and eliminate custom output procedures, but the issue persists.
Any assistance or insights into resolving these output issues would be greatly appreciated!
Thank you, Peter Cordes, for your invaluable feedback!
Your observation regarding the correct register usage for the WriteChar procedure was exactly what I needed to resolve the issues I was facing with my Pascal's Triangle program.
Initially, my program correctly displayed Pascal's Triangle up to Row 5. However, starting from Row 6 onwards, the output became garbled with concatenated numbers and random symbols. This was primarily due to incorrect handling of the space character between binomial coefficients.
As you pointed out, the WriteChar procedure from the Irvine32 library expects the character to be in the AL register, not DL. In my original code, I was moving the space character into DL, which led to incorrect character printing.
Corrected Register for WriteChar:
Original Code:
; Print Space
MOV DL, 32 ; ASCII space character (decimal 32)
CALL WriteChar ; Print space
Updated Code:
; Print Space
MOV AL, 32 ; ASCII space character (decimal 32)
CALL WriteChar ; Print space
Explanation:
By moving the space character (32) into the AL register instead of DL, the WriteChar procedure correctly prints the space, ensuring proper separation between binomial coefficients.
Verified Register Preservation:
EAX, EDX, ESI, EDI) are properly preserved at the beginning of procedures and restored before exiting. This prevents unintended side effects from procedure calls like WriteDec and WriteChar.After implementing the changes, the program now correctly displays Pascal's Triangle with proper spacing between numbers. Here's an example of the output when entering 13 rows:
Pascal's Triangulator - Programmed by Cameron Brooks!
This program will print up to 13 rows of Pascal's Triangle, per your specification!
Enter total number of rows to print [1...13]: 13
Row 0: 1
Row 1: 1 1
Row 2: 1 2 1
Row 3: 1 3 3 1
Row 4: 1 4 6 4 1
Row 5: 1 5 10 10 5 1
Row 6: 1 6 15 20 15 6 1
Row 7: 1 7 21 35 35 21 7 1
Row 8: 1 8 28 56 70 56 28 8 1
Row 9: 1 9 36 84 126 126 84 36 9 1
Row 10: 1 10 45 120 210 252 210 120 45 10 1
Row 11: 1 11 55 165 330 462 462 330 165 55 11 1
Row 12: 1 12 66 220 495 792 924 792 495 220 66 12 1
Thank you for using Pascal's Triangulator. Goodbye!
Understanding Library Procedures:
It's crucial to thoroughly understand how library procedures like WriteChar expect their arguments. Misplacing data in the wrong registers can lead to unexpected behaviors.
Register Management:
Proper preservation and restoration of registers are essential to maintain data integrity across procedure calls in Assembly language.
Thanks to Peter's guidance, the program now functions as intended, accurately displaying Pascal's Triangle with proper spacing between numbers. If anyone has further suggestions or improvements, I'd be happy to hear them!