reading string each number c#

Question

suppose this is my txt file:

line1
line2
line3
line4
line5

im reading content of this file with:

 string line;
List<string> stdList = new List<string>();

StreamReader file = new StreamReader(myfile);
while ((line = file.ReadLine()) != null)
{                
    stdList.Add(line);           
}
finally
{//need help here
}

Now i want to read data in stdList, but read only value every 2 line(in this case i've to read "line2" and "line4"). can anyone put me in the right way?

Answer 1

Even shorter than Yuck's approach and it doesn't need to read the whole file into memory in one go :)

var list = File.ReadLines(filename)
               .Where((ignored, index) => index % 2 == 1)
               .ToList();

Admittedly it does require .NET 4. The key part is the overload of Where which provides the index as well as the value for the predicate to act on. We don't really care about the value (which is why I've named the parameter ignored) - we just want odd indexes. Obviously we care about the value when we build the list, but that's fine - it's only ignored for the predicate.

Answer 2

You can simplify your file read logic into one line, and just loop through every other line this way:

var lines = File.ReadAllLines(myFile);
for (var i = 1; i < lines.Length; i += 2) {
  // do something
}

EDIT: Starting at i = 1 which is line2 in your example.