Change for loop to Parallel.For loop

Question

I can change my loop

for (int i = 0; i < something; i++)

to:

Parallel.For(0, something, i =>

But how to do this with this loop?:

for (i = 3; i <= something / 2; i = i + 2)

Thanks for answers.

Answer 1

Since

for (int i = 3; i <= something / 2; i = i + 2)
{
    ...
}

can be rewritten into

for (int k = 1; k < (something + 2) / 4; ++k)
{
    int i = 1 + 2 * k;
    ...
}

you can put

Parallel.For(1, (something + 2) / 4, k =>
{
    int i = 1 + 2 * k; 
    ... 
});

Answer 2

The third parameter is a delegate. So every iteration you could specify what your indexing variable shall do inside the delegate.

EDIT: Ok found a working solution: As already suggested by Dmitry Bychenko you should still start from 0 and just add the startValue as an offset

int something = 16;

int startValue = 3;
int stepSize = 2;

List<int> numbers = Enumerable.Range(0, 20).ToList();

Parallel.For(0, something / 2, i => 
{
    int ind = (stepSize * i) + startValue ; Console.WriteLine(numbers[ind]);
});