Experiencing Infinite Loop with Right Triangle Program in MASM Assembly Language
I'm currently trying to make a program in MASM assembly language that will print out a series of right triangles based on an integer value that the user inputs. For example, if the user input is 3 then the program will output:
*
* *
* * *
-
* * *
* *
*
-
*
* *
* * *
-
* * *
* *
*
I have figured out all of the triangles except the third one. I'm experiencing an infinite loop with spaces1 under triangle 3. The program will print out the triangle correctly up until it reaches one less than what the user integer value is, and then it loops spaces for infinity. I've been working on this for a while and I'm not sure how to fix this error. Here's my code:
org 100h
.model small
.stack 16
.data
; question the user is asked
input db "Enter the size for the triangles between 3 and 9, or 0 to quit $"
size dw ?
.code
main proc
mov AX, @data ; move location of data segment into AX
mov DS, AX ; points ds register at data segment
prompt:
mov AH, 09h ; opcode to print string
lea DX, input ; string to print out
int 21h
mov AH, 01h ; opcode to read in single char
int 21h
cmp AL, '0' ; check to see if user wants to quit
je exit
sub AL, '0' ; convert user input to literal value
mov AH, 0 ; blank out top half of AX
mov size, AX ; make copy of user input as literal value
mov CX, AX
mov BX, 1 ; sets up BX register for star counter loop
call crlf
; First Triangle
lines1:
push CX ; store the outer (lines) loop
mov CX, BX ; the number of stars to print out
stars1:
mov AH, 02h ; opcode to print string
mov DL, '*' ; char to print out
int 21h
loop stars1 ; end loop
call crlf
inc BX ; increment BX (stars)
pop CX ; recover value from CX for the outer lines loop
loop lines1 ; end loop
call crlf
mov CX, size ; reload CX with copy of size for next triangle
mov BX, 1
; Second Triangle
lines2:
push CX ; store the outer (lines) loop
stars2:
mov AH, 02h ; opcode to print single char
mov DL, '*' ; char to print out
int 21h
loop stars2 ; end loop
call crlf
pop CX ; recover value for outer loop
loop lines2 ; end loop
call crlf ; call crlf proc
mov CX, size ; reload CX with copy of size for next triangle
mov BX, 1 ; set up BX for star loop
; Third Triangle
lines3:
push CX ; Store the outer loop counter
mov CX, size ; Calculate spaces needed
sub CX, BX ; Adjust CX for the number of spaces
spaces1:
mov AH, 02h ; Opcode to print single char
mov DL, ' ' ; Print a space
int 21h
loop spaces1 ; End loop for spaces
mov CX, BX ; Set number of stars for this line
stars3:
mov AH, 02h ; Opcode to print single char
mov DL, '*' ; Print a star
int 21h
loop stars3 ; End loop for stars
call crlf ; Move to the next line
inc BX ; Increment the number of stars for the next line
pop CX ; Restore outer loop counter
loop lines3 ; End outer loop
call crlf ; call crlf proc
mov CX, size ; set up CX for fourth triangle
mov BX, 1
; Fourth Triangle
lines4:
push CX ; store copy of CX for outer loop
mov CX, BX ; set up number of spaces for spaces loop
spaces2:
mov AH, 02h ; opcode to print char
mov DL, ' ' ; char to print out
int 21h
loop spaces2 ; end loop
pop CX ; recover CX for stars loop
push CX ; for outer lines loop
stars4:
mov AH, 02h ; opcode to print char
mov DL, '*' ; char to print out
int 21h
loop stars4 ; end loop
call crlf
inc BX ; increment BX for next line
pop CX ; recover value for outer lines loop
loop lines4
call crlf ; call crlf proc
mov CX, size ; set up CX for fourth triangle
mov BX, 1
exit:
mov AX, 4C00h
int 21h
main endp
crlf proc
mov AH, 02h ; opcode to print single char
mov DL, 13 ; ASCII carriage return
int 21h
mov DL, 10 ; ASCII line feed
int 21h
ret
crlf endp
end main
Here's a screenshot of the issue. In the program it's looping between lines 92 and 95 in spaces1
Could someone point me in the right direction? Thanks! :)
Solution
Both the 3rd and the 4th triangles have a line where no space has to be inserted. You need to add a suitable by-pass of the spaces1 and spaces2 loops.
mov CX, size
mov BX, 1
; Third Triangle
lines3:
push CX
mov CX, size
sub CX, BX ; If this subtraction produces 0 then
jz SkipSpaces1 ; this jumps over (so skips) the spaces1 loop
spaces1:
mov AH, 02h
mov DL, ' '
int 21h
loop spaces1
SkipSpaces1:
mov CX, BX
In case of the 4th triangle, set up BX=0 because there's no space on the very first line:
mov CX, size
mov BX, 0
; Fourth Triangle
lines4:
push CX
mov CX, BX ; If this loads CX with 0, then
JCXZ SkipSpaces2 ; this jumps over (so skips) the spaces2 loop
spaces2:
mov AH, 02h
mov DL, ' '
int 21h
loop spaces2
SkipSpaces2:
pop CX
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