Using conditional operator in lambda expression in ForEach() on a generic List?

Question

Is it not allowed to have a conditional operator in a lambda expression in ForEach?

List<string> items = new List<string>{"Item 1", "Item 2", "Item I Care About"};

string whatICareAbout = "";

// doesn't compile :(
items.ForEach(item => item.Contains("I Care About") ? 
whatICareAbout += item + "," : whatICareAbout += "");

Compilation error -> "Only assignment, call, increment, decrement, and new object expressions can be used as a statement"

Trying to use a normal if doesn't work either:

// :(
items.ForEach(item => if (item.Contains("I Care About")) {whatICareAbout += item + ", ";}

Just not possible?

Answer 1

You're using the shorter form of lambda expressions, which only allow a single expressions.
You need to the long form, which allows multiple statements.

For example:

items.ForEach(item => {
    if (item.Contains("I Care About")) 
        whatICareAbout += item + ", ";
});

Answer 2

What are you trying to acheive? Are you trying to form a string of comma separated items where they contain a particular value? In linq you would achieve this using the following:

 List<string> items = new List<string> { "Item 1", "Item 2", "Item I Care About", "Item I Care About", "Item I Care About" }; 
 string whatICareAbout = items.Where(x => x.Contains("I Care About"))
                              .Aggregate( (y, z) => y + ", " + z);

The output from this is "Item I Care About, Item I Care About, Item I Care About".

Note: Aggregate is a great way of ensuring there is no trailing ","