switch the value of variable javascript

Question

I have two variables M & N and with certain condition in my loop I want to switch the value of N between itself and M. So the following code came in my mind

MxN = M * N;

N = MxN/N;

But values of M and N may be 2 000 000 000. Therefore Im in doubt. Is that fine variant to switch between such a huge values or may be its better(faster) to

counter = 2;
N = counter % 2 == 0 ? M : N; 
counter++;

edit Sorry I didn't mention that I dont want to affect the value of M
Thanks everyone)

You can't do "temp = M; M = N; N=temp;"? Am I misunderstanding your question? — Pete
– Pete, Commented Mar 8, 2013 at 15:05
@SakerONE Could you please add an example of input->output to your question? — Ron van der Heijden
– Ron van der Heijden, Commented Mar 8, 2013 at 15:09
input M = 3; N = 5; at first iteration of the loop N - 3 at second N - 5 at third N - 3 and so on — Artem Svirskyi
– Artem Svirskyi, Commented Mar 8, 2013 at 15:11

Ron van der Heijden · Accepted Answer · 2013-03-08 15:42:04Z

2

There are so many ways.

1 http://jsfiddle.net/8NvVf/

m -= n
n += m
m = n - m

2 http://jsfiddle.net/eQGwL/ (Only works in FireFox and maybe Rhino)

[n, m] = [m, n]

3 http://jsfiddle.net/4MQXe/

m = (n += m -= n) - m

Edit

If you don't want to change the value of m you need a temp value.

http://jsfiddle.net/Yjkn3/

var n = 5
var m = 8
var t = n

for (var i = 0; i < 10; ++i) {
    if(n != m) n = m
    else n = t
    console.log(n + ' ' + m)
}

edited Mar 8, 2013 at 15:42

answered Mar 8, 2013 at 15:16

Ron van der Heijden

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2 Comments

Lekensteyn Over a year ago

Hmm, I didn't know that it was also to do such swap trick using arrays in Javascript. Is that a new language feature or something that existed "since the beginning"?

Artem Svirskyi Over a year ago

Sorry I didn't mention that I dont want to affect the value of M

Lekensteyn · Accepted Answer · 2013-03-08 15:06:10Z

1

Both approaches are suspect to an integer overflow (and the earlier one also to precision errors). Why not limit the range of the counter and adapt the second approach?

state = 0;
switch (state) {
case 0:
    // ...
    break;
case 1:
    // ...
    break;
// ...
}

state = state < maxState ? state + 1 : 0;

It is up to you to optimize this, but please keep readability and maintainability in mind. An alternative to this switch is to use an array.

For two variables, please do not mess with xor hacks when trying to swap variables, just write what you want:

var temp = N;
N = M;
M = N;

answered Mar 8, 2013 at 15:06

Lekensteyn

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Comments

Daedalus · Accepted Answer · 2013-03-08 15:06:14Z

0

The classic trick for swapping two values is to use XOR:

x = x xor y
y = x xor y
x = x xor y

answered Mar 8, 2013 at 15:06

Daedalus

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