format  PE      Console 
entry   start                   

include 'C:\FASM\INCLUDE\win32a.inc'

macro set_ascii_code number, quantity_of_digits
{
        local looping
        
        xor ecx, ecx
        xor eax, eax
        xor edx, edx
        
        or ecx, quantity_of_digits ;Command loop will use register ecx
looping : 
        mov dh, [number + eax]
        or dh, 030h
        mov [number + eax], dh
        inc eax
loop looping
}


section '.data' data readable writeable
first_number db 1,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9 
first_number_length   =   $ - first_number 
max_length dw 0

second_number db 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1
second_number_length = $ - second_number  

result db 100 dup(0)

handle_to_output_stream dd 0
reserved dd 0
symbols_was_written dd 0

section '.code' code readable executable
start:
        push eax
        push ebx 
        push ecx
        push esi
        push ebp
        push esp
        push edx 
        
        invoke GetStdHandle, STD_OUTPUT_HANDLE
        mov [handle_to_output_stream], eax 
        
        if first_number_length >= second_number_length
                mov eax, second_number_length
                mov esi, first_number_length 
        else
                mov eax, first_number_length
                mov esi, second_number_length 
        end if
        mov ecx, eax
        
        dec esi
        mov ebp, first_number_length
        mov esp, second_number_length 
        
        dec ebp
        dec esp 
        
        xor eax, eax
        xor ebx, ebx
        xor edx, edx

        
        mov al, [first_number+ ebp]
        mov ah,[first_number+ ebp - 1] 
        shl ah, 4 
        or al, ah 
        
        add al, [second_number+ esp] 
        daa 
        adc ah, 0
        
        or dl, al 
        and dl, 0Fh 
        mov [result+esi], dl 
        
        shr ax, 4 

        dec esi
        dec esp
        
        dec ebp 
        dec ebp
        
        dec ecx 
        
        xor dl, dl
        
for_looping : 
        dont_get_last_digit : 
        
        mov ah,[first_number+ebp] 
        shl ah, 4
        or al, ah 
        
        add al, [second_number+esp] 
        daa 
        adc ah, 0
        
        or dl, al 
        and dl, 0Fh 
        mov [result+esi], dl
        
        CMP esp, 0
        je break1
        
        CMP esi, 0
        je break2
        
        dec esi
        dec esp
        shr ax, 4
        xor dl, dl
        
        CMP ebp, 0
        je dont_get_last_digit
        
        dec ebp
loop for_looping

break1 : 
break2 :

        set_ascii_code result, first_number_length
        invoke WriteConsole, [handle_to_output_stream],result, first_number_length, symbols_was_written , reserved
        
        
FINISH :
    pop eax
        pop ebx 
        pop ecx
        pop esi
        pop ebp
        pop esp
        pop edx 
                
        invoke  ExitProcess, 0
        
section '.idata' import readable
        library kernel, 'KERNEL32.DLL',\
                        ascidc,         'ascidc.dll'
import  kernel,\        
                        ExitProcess,    'ExitProcess',\
                        GetStdHandle,   'GetStdHandle',\
                        WriteConsole,   'WriteConsoleA',\
                        GetCurrentDirectory,    'GetCurrentDirectoryA',\
                        CloseHandle,    'CloseHandle',\
                        CreateFile,             'CreateFileA',\
                        ReadFile,               'ReadFile',\
                        WriteFile,              'WriteFile',\
                        GetCommandLine, 'GetCommandLineA',\
                        VirtualFree,    'VirtualFree',\
                        VirtualAlloc,   'VirtualAlloc',\
                        SetFilePointer, 'SetFilePointer',\
                        GetFileSize,    'GetFileSize',\
                        ReadConsole,    'ReadConsoleA'
                        
import  ascidc,\
                        GetSPSTR,       'GetSPSTR',\
                        ASCIINH,                'ASCIINH',\
                        NHASCII,                'NHASCII'     

PUSH and POP must be in reverse order from each other.

BTW: For Windows you only need to preserve EBX, EBP, ESI and EDI.

push eax
        push ebx 
        push ecx
        push esi
        push ebp
        push esp
        push edx 
..................................
FINISH :
        pop edx
        pop esp
        pop ebp
        pop esi
        pop ecx
        pop ebx
        pop eax

    

It probably isn't a good idea to be PUSHing or POPing ESP. Also you can't use ESP as a general purpose register like that. Remember that ESP is the stack pointer so after you change it your stack is now lost.

Remember that ESP is the stack pointer so after you change it your stack is now lost.

Sloppysecond, it is better to use pushad and popad in your situation. It preserves/restores all registers in one command.

When you PUSH you save the value on the stack, and later you POP to recover the original value. It is part of the Windows calling standard, all functions are expected to not corrupt EBX, EBP, ESI and EDI.