NASM Linux Assembly Printing Integers

Question

I am trying to print a single digit integer in nasm assembly on linux. What I currently have compiles fine, but nothing is being written to the screen. Can anyone explain to me

Answer 1

This is adding, not storing:

add edx, ecx        ; stores ecx in edx

This copies ecx to eax and then overwrites it with 4:

mov eax, ecx        ; moves ecx to eax for writing
mov eax, 4          ; sys call for write

EDIT:

For a 'write' system call:

eax = 4
ebx = file descriptor (1 = screen)
ecx = address of string
edx = length of string