Get an index of item from List<int>, when all of items are the same?

Question

Im trying to do foreach for my purposes.

My scenerio looks like this:

I have a list and it looks like this (with only two values, 255 and 0):

List<int> list = new List<int>(){ 255, 0, 0, 255, 0, 255, 255, 0, 255 };

And a loop:

foreach(var item in list)
{
      if(item == 255)
      {
           counter++; //its simple 'int' varialbe 
           summary += secondList.Contains(item); //its second list with ints
      }
}

My secondList looks like this:

static List<int> secondList= new List<int>(){ 128, 1,  2, 64,  0,  4, 32,  16, 8 };

What i want to do, is according to index of item add value with the same place from secondList .

If index of item == 1, i want to set secondList to position "1" too and add its value to summary variable.

As i know, Contains will return first item as item but like you see, in list i storage only two values, 255 and 0.

Is it possible to get the index of item in foreach loop properly?

Answer 1

Either declare a variable that will hold the index , or use a foor loop instead:

int idx = 0;
foreach(var item in list)
{
      if(item == 255)
      {
           counter++; //its simple 'int' varialbe 
           summary += secondList[idx];
      }

    idx++;
}

Answer 2

Simplest solution is to use for loop.

int counter = 0;
int summary = 0;

List<int> list = new List<int>() { 255, 0, 0, 255, 0, 255, 255, 0, 255 };
List<int> secondList = new List<int>() { 128, 1, 2, 64, 0, 4, 32, 16, 8 };

for (int i = 0; i < list.Count; i++)
{
    if (list[i] == 255)
    {
        counter++; //its simple 'int' varialbe 
        summary += secondList[i]; //its second list with ints
    }
}

Answer 3

You could also use a more functional approach, like

List<int> list = new List<int>(){ 255, 0, 0, 255, 0, 255, 255, 0, 255 };
List<int> secondList= new List<int>(){ 128, 1,  2, 64,  0,  4, 32,  16, 8 };

var matches = list.Zip(secondList, Tuple.Create)
                  .Where(t => t.Item1 == 255)
                  .Select(t => t.Item2);

Console.WriteLine(matches.Count());
Console.WriteLine(matches.Sum());

Output:

5
236