Assembly lowercase to uppercase no display

Question

I am trying to code a simple program that converts the lowercase characters of a string to uppercase but I get no output at all. For example:

Input:AaBb Output:AABB

I don't know where my mistake is but anyway, My code is:

data segment
prompt db 0dh,0ah,"Your string: $"
str1 db 15 dup('$')
msg db 0dh,0ah,"Result after conversion: $"
data ends

code segment
assume cs:code,ds:data
START:
mov ax,data
mov ds,ax

mov dx,offset prompt
mov ah,09h
int 21h

mov ah,01h
lea dx,str1

read:
int 21h
mov bl,al
cmp al,0Dh
je display1
cmp al,61h
jl nexx
cmp al,7Ah
jg nexx

sub al,20h
mov [si],al
inc si
jmp read

display1:

lea dx,msg
mov ah,09h
int 21h

lea dx,str1
mov ah,09h
int 21h

mov ah,4ch
int 21h

nexx:
inc si
jmp read

code ends
end start

You use `si` to store the value, but I cannot see where you load the address into it. — Bo Persson, Aug 06 '16 at 13:35
Learn to use a debugger so you can single-step through your code and find the problem yourself. Giving no output doesn't tell you nearly enough about where the problem might be. — Peter Cordes, Aug 06 '16 at 15:18
There are [more efficient ways to upcase](http://stackoverflow.com/a/35936844/224132). But that's probably not even your bug if you're not getting any output. — Peter Cordes, Aug 06 '16 at 15:26

score 0 · Answer 1 · answered Aug 06 '16 at 16:47

0

You forgot to point si to str1 before getting input characters

mov ah,01h
lea dx,str1 
mov si,dx    ;point si to str1

and you forgot to save non converted uppercase characters to output string

nexx: 
mov [si],al
inc si
jmp read

answered Aug 06 '16 at 16:47

rcd

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Assembly lowercase to uppercase no display

1 Answers1