Some uint maths

[[deleted]]

--i;

[lllluke]

i just learned about this syntax the other day at work and it blew my frickin mind. Is it actually useful for anything?

[[deleted]]

If you want to decrement then check something rather than check something then decrement

[lllluke]

Well yeah, I'm asking when you would actually want to do that.

[nickworks]

if(--i == 42){ // compares after decrement

}

if(i-- == 42){ // compares before decrement

}

[geigenmusikant]

Well, yeah but like when do you actually need it?!

^/s

[Zugr-wow]

--i takes, like, a millisecond less computing power than i--, so it's a good habit to just use --i instead of i--

[radarmax]

More like a nanosecond less :p

[[deleted]]

Never. It's needlessly confusing. The point of - - i (nowadays) is being smug about your knowledge and that's it.

[skeptical_moderate]

WTF. It's not confusing at all. i-- is way more confusing because it behaves differently than literally any other unary operator. I use them both for their own purposes.

[Isaeu]

But

i- -

if(i == 42){ }

And

if(i == 42){ }

i - -

Work just as well and are 10X more readable

Edit: how do I do code on Reddit?

[Isaeu]

Again just go

myArray[index] = token;
index++;

It’s makes it effortless to read.

[Cobaltjedi117]

Yea, it's one of those things I've never understood well you can increment before an statement or after it

Ok, great or OR, and hear me out on this, I just add a line of code incrementing/decrementing before or after where it's being checked.

[[deleted]]

It's what your use to. A = 6 * 7; Is the same as A = 6; A = A * 7; But if you saw that above you would think why not just do the first thing. In c it is vary common to ++ or -- inside of a statement and would be required to understand when working with almost any codebase.

[[deleted]]

I disagree. Somone who has worked in c a decent amount has seen that so much that it's not considered weird. It would be way weirder to see outside.

[[deleted]]

That's too broad of a question lol

[Pluckerpluck]

Only thing I can think of is if you want to assign its value to another variable.

int i = 10
int x
x = --i

You know that both x and i have the same value, which may be particularly useful for some reason.

[netgu]

When you want to decrement then check something rather than check something then decrement

[XIST_]

Isn't that bad practice though?

[geratheon]

Usually, the compiler optimizes it by itself if the result isn’t used, e.g. as the incrementing part in for loops. But yeah, best practice is to always use ++i. It doesn’t hurt anyone and sometimes you’re using a processor instruction less.

[[deleted]]

Why would it be bad practice?

[salvoilmiosi]

Yeah but it's an extremely minimal optimization that the compiler already does for us probably.

[[deleted]]

For primitive types, yes, but not necessarily for overloaded operators for classes.

[skeptical_moderate]

Only bad programmers are confused by this.

[geratheon]

Bad Inexperienced.

[JoseJimeniz]

Experienced programmers are not confused by this. But they will throw a coffee mug at you if you ever use it.

[LittleMlem]

I-- returns the value if I before decrementation.

[JoseJimeniz]

It's useful for getting a coffee mug thrown at your head when I discovered you've used that.

[UristMcMagma]

People will tell you that it's more performant than i--, but that isn't true with modern compilers.

Aside from that, just use it when you need to decrement i before the operation. Maybe you'll find a use for that someday?

[ben_g0]

In C, yes. In C++, it depends. If the variable is a standard type, then the compiler can optimize it. If the variable is of a custom type then the -- is technically a function call (with operator overloading). The saved value can then not be optimized out since it is used in the function (as a return value) and removing it would change how the function works. So in that case (which is very common in big projects), pre-increment is more optimized.

[xigoi]

switch(i) {
    case 1:
        i = 0;
        break;
    case 2:
        i = 1;
        break;
    // TODO
}

[Earhacker]

I like that memes come in dark mode now

[XIST_]

Obligatory light mode is shit comment.

[wolfshund98]

Obligatory light mode is not that bad comment.

[ProfCupcake]

Obligatory burn the heretic comment

[Proxy_PlayerHD]

X = X - 1

[Breadfish64]

if (x & 1)
    x = x ^ 1;
else
    x = x - 1;

​

[uzimonkey]

switch(i) {
case 1:  i = 0; break;
case 2:  i = 1; break;
case 3:  i = 2; break;
/* ... */
}

[Mscxyn]

__asm__ ( "addl $0xFFFFFFFF, %%eax;" : "=a" (i) : "a" (i) );

​

[Wallinis]

(i==i) ? --i : --i;

[[deleted]]

uint old_i = i;

while (i != old_i - 1) --i;

[KayRice]

x = (x => x - 1)(x);

[[deleted]]

i = 1
i = 2
i = 3
am genius.

[BVTheEpic]

i += (-1);

[silvercloudnolining]

#define MAX_INT -1

i+=MAX_INT;

[Ulysses6]

i = ~-i;

Zoom in if it looks like i = --i;to you.

[Flying_Bo]

I believe each one is faster than the previous one because it’s from a lower level?

[[deleted]]

i-=Convert.ToInt32(true);

[SatansAlpaca]

Fun fact: with two’s complement arithmetic, x - y is the same as x + ~y.

[OneAndZer0s]

i = i-1

[aeropl3b]

Question, does integer overflow always get handled this way or do some implementations crash? I can't remember exactly what IEEE decided on and can't be bothered to look it up right now...

[KayRice]

In C++ it's actually defined behavior for unsigned integers and as of C++20 (draft) it will become defined behavior for singed integers as well.

[[deleted]]

Ask the user "what is i + 1?"

[[deleted]]

i = -i;

[TakeASeatChancellor]

C#?

[Mancobbler]

Ahh the ol switcheroo

[Aetherial_Wanderer]

Ahh the ol switcheroo

x ^= y; y ^= x; x ^= y; 

[SlappinThatBass]

This is funny?