C++ how to give "array -1" a value

[reisbro]

Simple question, I have this:
double percentMax[4] = {0.25, 0.40, 0.80, 1.50};

and I want to make a uniform_random(x, y) where:
x = percentMax[i-1]
y = percentMax[ii] <- I put double i here otherwise the forum would interpret it as italic

but If my i = 0, there is no i = -1 since 0 is the first space of the array.
I managed to do what I want but the code got pretty big, and I am pretty sure there is a simpler way hehe

 

[StreamSide]

what about math.max(0, i-1)

 

[Shyzoul]

what about math.max(0, i-1)

he is using C++ not lua

but If my i = 0, there is no i = -1 since 0 is the first space of the array.

x = percentMax[i > 0 ? i : 0]

 

[reisbro]

what about math.max(0, i-1)

but the problem is that for i == 0, i-1 does not exist, and when I call i -1 (or test[-1]) it will receive a random value right?

 

[reisbro]

he is using C++ not lua

perfect! I had to do a quick study because I never used ? before, but I think I understand it now.

if i > 0 i, else 0 right?

 

[Shyzoul]

perfect! I had to do a quick study because I never used ? before, but I think I understand it now.

if i > 0 i, else 0 right?

right, but the way i think while writing it:
boolean_condition ? if_true_condition : if_false_condition

 

[reisbro]

Oh I think that if I use it like this, when i is not >0 then x = percentMax[0] and not x = 0... That means x = 0.25
However I need x = 0 if i = 0

 

[StreamSide]

is he using c++? didnt knew it
also @reisbro math.max(0, i-1) will only choose 0 as max value
also std max will also work if you using c++
[std::max(0, i-1)]

 

[reisbro]

maybe uniform_random (0 ? i=0 : percentMax[i-1], percentMax[ii])?

again, the [ii] <- double i is just so the forum doesn't think I want to write italic haha

 

[reisbro]

is he using c++? didnt knew it
also @reisbro math.max(0, i-1) will only choose 0 as max value

oh I misread it! I accidentally read it like math.max(o, percentMax[i-1])
it would probably work too!

 

[Shyzoul]

However I need x = 0 if i = 0

i thought you was having problem with indexing, however

x = i < 0 ? 0 : percentMax[i];

 

[StreamSide]

i thought you was having problem with indexing, whatever
x = i < 0 ? 0 : percentMax;

what about max?
I mean std::max

 

[Ziker]

Just push whatever you want to be at -1 to 0, pushing the rest of values further? And start your loop from 1 (so you get x = 0, y = 1). Like this:

double percentMax[5] = {0.0, 0.25, 0.40, 0.80, 1.50};

for(int i = 1; i < 5; i++) {
   uniform_random(parcentMax[i-1], percentMax[i]);
}

 

[Shyzoul]

I mean std::max

for sure could work, but this is a simple thing, and usually compiler optimizer can't inline STL functions, due all polymorphism c++ thing, functions that are not inlined doesn't make cpu quite happy, tho i'm not sure about ::max

 

[reisbro]

Just push whatever you want to be at -1 to 0, pushing the rest of values further? And start your loop from 1 (so you get x = 0, y = 1). Like this:

double percentMax[5] = {0.0, 0.25, 0.40, 0.80, 1.50};

for(int i = 1; i < 5; i++) {
   uniform_random(parcentMax[i-1], percentMax[i]);
}

wow this is the simplest solution ever haha