INCLUDE Irvine32.inc

.data
Prompt1 BYTE "Input Text:", 0
Prompt2 BYTE "Caesar Cipher Output:", 0
UserInput BYTE 80 DUP (?)

.code
main PROC
	;print out the prompt
	mov edx, OFFSET Prompt1
	call WriteString
	call crlf

	;get a string from the user at most 79 letters
	mov ecx, 79
	mov edx, OFFSET UserInput
	call ReadString


	call crlf

	;print out the output text first before doing the cipher
	mov edx, OFFSET Prompt2
	call WriteString
	call crlf

	;point edx to the first letter
 	mov edx, OFFSET UserInput
A0:
	;get the letter at edx, if it equals 0, it's the last letter so exit (to the A1 label)
	mov al, [edx]
        cmp al, 0
        je  A1

	;if al is uppercases, make it lowercase
	.IF (al >= 'A') && (al <= 'Z')
		add al, 'a'-'A'
	.ENDIF

	;only if al is lowercase do the cipher
	.IF (al >= 'a') && ( al <= 'z')
                add al, 3
		;if it wrapped around, subtract
                .IF (al > 'z')
			sub al, 'z'-'a'+1
		.ENDIF
	.ENDIF

	;print out the letter
	call writeChar

	;point to the next letter and go back to the loop
	add edx, 1
        jmp A0
 A1:
	;get out
        call crlf
 	exit
 main ENDP
 END main