.data 
moo      db "Easy conversion between STR<-->INT by bor0", 0 
mystring db "Mynumber equals to: " 
mynumber db "321", 0 
mystr2   db "Mynumber has been converted to decimal and is now being stored in eax.", 0 
mystr3   db "Mybuffer equals to: " 
mybuffer db 4 dup(0) 
.data? 
result dd ? 
.code 
start: 
invoke MessageBox,0,ADDR mystring,ADDR moo,0 
;;;;;;;;;STR to INT 
;;;;;;;;;;;;;;;;;;; 
movzx eax, byte ptr [mynumber] 
sub eax, 48 
mov ecx, 100 
mul ecx 
add result, eax 
movzx eax, byte ptr [mynumber+1] 
sub eax, 48 
mov ecx, 10 
mul ecx 
add result, eax 
movzx eax, byte ptr [mynumber+2] 
sub eax, 48 
add result, eax 
invoke MessageBox,0,ADDR mystr2,ADDR moo,0 
mov eax, result 
;;;;;;;;;INT to STR 
;;;;;;;;;;;;;;;;;;; 
xor edx, edx 
mov ecx, 100 
div ecx 
add eax, 48 
mov byte ptr [mybuffer], al 
mov eax, edx 
mov ecx, 10 
cdq 
div ecx 
add eax, 48 
mov byte ptr [mybuffer+1], al 
add edx, 48 
mov byte ptr [mybuffer+2], dl 
invoke MessageBox,0,ADDR mystr3,ADDR moo,0 
invoke ExitProcess, 0 
end start