Question

how to make a while loop in assembly?

Answer 1

You'll need something like the following structure:

label: <loop body>
...
<loop condition check>
<conditional branch to 'label'>
<loop's finished here>

Answer 2

can u please show me with a simple example that does all those things

Answer 3

which architecture? X86, amd64, MIPS?

Answer 4

x86

Answer 5

Here a simple example that calculates 2 * n:

movl $0, %eax # i = 0
movl $0, %ebx # result = 0
movl $10, %ecx # n = 10
jmp check # without this jmp, it'd be a do-while loop
loop:
addl $2, %ebx # result = 2 * result
addl $1, %eax # i++
check: cmp %ecx, %eax
jl loop # Jump if i < n

Btw, most compilers can also output assembly code. If you compile some C-code with gcc, you need to add the `-S` flag. Then, gcc will only generate ASM for you.

Answer 6

wat are this ( $)

Answer 7

i'm getting errors

Answer 8

There are two different syntaxes for writing x86 ASM: AT&T and Intel. The code I wrote is in AT&T syntax while your assembler probably expects Intel syntax.

@walters The $ is part of the AT&T syntax to indicate an immediate (or constant) value. % indicates a register.

A quick (but not tested yet) rewrite:

mov eax, 0
mov ebx, 0
mov ecx, 10
jmp check
loop:
add ebx, 2
add eax. 1
check: cmp eax, ecx
jl loop

Answer 9

that is why u have to analyse numbers correctly u'll get it

Answer 10

@slotema i get it

Answer 11

OOOH! I SEE IT! @slotema

Answer 12

@AuthenticationError WHAT DO YOU MEAN BY Numbers?

Answer 13

so using assembly @slotema how to do modulus because this is giving me errors
a mod b

Answer 14

like looping if x is even
is'nt i have to do modulus like in c and c+

Answer 15

If you really have different questions, you should start a new thread, so Mahlatse1 won't get a lot of notifications.

For modulo, you'll need to do a division. After e.g. `div eax, ebx`, eax will contain the quotient and edx will contain the remainder.

But divisions are costly. If you just want to check whether or not a number is even, there are faster ways of doing that. Like checking the LSB of the number (if it's 1, the number is odd).