Develop Reference

C# conditional operator - Call method if condition is true else do nothing

C# provides conditional operator (?:) that returns one of two values depending on the value of a Boolean expression. eg
condition ? first_expression : second_expression;
My question is can we use the same syntax to call a method when condition is true? and when condition is false then do nothing
public void Work(int? val)
{
var list = new List<int>();
//ofcourse line below doesn't work
//but is it possible to call method when condition is true and else do nothing
val.HasValue? list.Add(val.value) : else do nothing
}

the ?: has also been referred to as the ternary operator in the past. Ternary, for three. if this, then do this, else do this.
You have two expressions. If this, do this. This is exactly the point of an if statement. You are trying to fit your case into a construct that it isn't designed for. Don't do this.
Use the correct operation for the job:
if(val.HasValue)
{
list.Add(val.value)
}

The C# conditional operator is used to return a different value depending on the evaluation of a condition. It is not meant to be used to to be used the way you are trying to in your question. It should like be used this :
int test = i > 3 ? 0 : 1;
test will then equal 0 if i is less than (or equal to) 3, or test will equal 1 if 3 is greater than 3.
To do what you want you will have to use a regular if statement (which you can still write in one line by the way) :
if (val.HasValue) list.Add(val.value);

The conditional/ternary operator is supposed to return a value and that very specific value must be assigned back to somewhere.
So, in that case you can do that, yes. But, it would lead to bad design.
In a regular case, one would do this:
int x = (a > b) ? a : b;
Now, lets assume AddToList() is your desired method when the condition renders to true and DoRest() is the method you want to invoke if the condition turns out to false.
In the aforementioned case, you'd end up doing something like this:
int result = val.HasValue? AddToList(val.value) : DoRest();
Now you have to rely on result for finding out which one has been called (if you ever need that) and it's not very expressive and doesn't point to proper code design.
If you get a tad more adventurous you'd end up with :
var actionToInvoke = val.HasValue ? (Action)AddToList: (Action)DoRest;
actionToInvoke();
In any case, none of these lead to very readable code.
So, sticking with a simple if(val.HasValue) would be the simplest way to go here.

The way null conditional operator works is you have to return a value for the variable you are assigning it to. So if you would like a string value or something else other than void you can call the method with out any problem. But to call a void method you can use a delegate.
delegate void DelMethod();
void Method() { }
void MethodTwo() { }
private void MyMethod()
{
DelMethod x;
x = condition == true ? (DelMethod)Method : (DelMethod)MethodTwo;
}

Can't use ternary for return null

I want replicate this condition:
string responseText = getData();
if(responseText == null){ return; }
with the ternary operator, what I tried is:
responseText == null ? return : null;
but I get return underlined in red with:
return is not a valid term for the expression.
Essentially I want stop the code of this function with a return if responseText is null, instead if is different against null I need to continue my code. What I did wrong?

Ternary operator is used for assignment:
string a = isEmpty ? item : null; //this is OK
If you assign nothing, you cannot use the ternary operation.
response == null ? return : null; //what is this??
What you have done, is likely already correct:
if (responseText == null)
return;
//do something else when text is not null

The purpose of a ternary operator is to be able to create an expression that uses conditions.
It's not intended for controlling the flow of your program, and you shouldn't attempt to use it that way.
Stick with your if statement.

The ternary operator is an expression - it returns one value or the other based on the condition. You are trying to use it for program flow which is not possible.
I see nothing wrong with your if statement - is it clear, concise, and most importantly, it works.

You can't return return. The returned value must be a variable of the same type as the one receiving the ternary expression's result.

The ternary operator evaluates an expression. It cannot control the flow of your program. Your best bet is to use an old fashioned if statement, such as the one you provided in your question.

The operand of a ternary operator should be a expression yielding a value. But in this case return doesn't yields any value.

how do I convert if else to one line if else?

how do i convert follow code to one line if else
if (data.BaseCompareId == 2)
report.Load(Server.MapPath("~/Content/StimulReports/MonthGroup.mrt"));
else
report.Load(Server.MapPath("~/Content/StimulReports/YearGroup.mrt"));
i try this code but did not work
data.BaseCompareId == 2
? report.Load(Server.MapPath("~/Content/StimulReports/MonthGroup.mrt"))
: report.Load(Server.MapPath("~/Content/StimulReports/YearGroup.mrt"));

Try with this instead :
string path = data.BaseCompareId == 2
? "~/Content/StimulReports/MonthGroup.mrt"
: "~/Content/StimulReports/YearGroup.mrt";
report.Load(Server.MapPath(path));
Since report.Load() returns a void, it wont work.
Edited version :
string s = data.BaseCompareId == 2
? "MonthGroup.mrt"
: "YearGroup.mrt";
report.Load(Server.MapPath("~/Content/StimulReports/" + s));

I am assuming report.Load returns a void, hence it "doesn't work". That said, why are you doing this? The first example is perfectly clear.

If you want are going to use ?: here use it so only the part which is actually different is in the branching statement:
string fileName = (data.BaseCompareId == 2) ? "MonthGroup.mrt" : "YearGroup.mrt";
report.Load(Server.MapPath("~/Content/StimulReports/" + fileName));

If you want to use a ternary operator, you can do:
report.Load(data.BaseCompareId == 2 ? Server.MapPath("~/Content/StimulReports/MonthGroup.mrt") : Server.MapPath("~/Content/StimulReports/YearGroup.mrt"));
Or (better):
report.Load(Server.MapPath(data.BaseCompareId == 2 ? "~/Content/StimulReports/MonthGroup.mrt" : "~/Content/StimulReports/YearGroup.mrt"));
(Or you could further exploit the similarity in the two strings, as #helb's answer does.)
As has already been noted, your way doesn't work because you're trying to replace a conditional statement with a conditional expression, and conditional expressions have to have a value. Since report.Load apparently returns void, a conditional expression of the form cond ? report.Load(...) : report.Load(...) doesn't have a value, ergo it doesn't work.
Each of the ways above will work because the conditional expressions in them have values - in the first case, the value will be of the type returned by Server.MapPath; in the second case, the value will be of type string.
As to whether you should do this: there are arguments to be made either way. The original way has the advantage of being clear and simple, but it does involve some (arguably undesirable) repetition. The latter approach above has the advantage of only saying things once and emphasising the intent of the whole statement (to load a report), but it's arguably slightly less clear than the original, depending on how used people are to seeing conditional expressions. YMMV.

This syntax is just for cases where it returns something. So you could do something like:
var path = (data.BaseCompareId == 2) ? "~/Content/StimulReports/MonthGroup.mrt" : "~/Content/StimulReports/YearGroup.mrt";
report.Load(Server.MapPath(path));

This is the most concise I could get for a one-liner...
report.Load(Server.MapPath(string.Format("~/Content/StimulReports/{0}Group.mrt", data.CompareId == 2 ? "Month" : "Year")));
However, it seems you just want to make things look cleaner.
More abstraction between data calls and the conditional logic.
You might want to consider making them separate methods, perhaps on your report object?
if(data.CompareId == 2)
report.LoadStimulReports(ReportGroup.Month);
else
report.LoadStimulReports(ReportGroup.Year);
Using an enum, extension method, and static method on your report object...
public enum ReportGroup
{
[DescriptionAttribute("~/Content/StimulReports/MonthGroup.mrt")]
Month,
[DescriptionAttribute("~/Content/StimulReports/YearGroup.mrt")]
Year
}
public static T GetAttribute<T>(this Enum e) where T : Attribute
{
System.Reflection.FieldInfo fi = e.GetType().GetField(e.ToString());
object[] o = (object[])fi.GetCustomAttributes(typeof(T), false);
return o.Length > 0 ? (T)o[0] : default(T);
}
public static void LoadStimulReports(ReportGroup reportGroup)
{
report.Load(Server.MapPath(reportGroup.GetAttribute<DescriptionAttribute>().Description));
}
Now you can simply add another item to the enum if you need another report.
[DescriptionAttribute("~/Content/StimulReports/WeekGroup.mrt")]
Week

Confusing code with ? operator

I was reading through someones old code and I found this line:
menuItem.Checked = (menuItem.Checked == false) ? true : false;
I dont understand what it does and how. any help?

It's a complicated way to write:
menuItem.Checked = !menuItem.Checked;

Take a look at Conditional Operator: ? :
This means:
if(menuItem.Checked == false)
{
menuItem.Checked = true;
}
else
{
menuItem.Checked = false;
}

Your statement means:
if(menuItem.Checked == false)
menuItem.Checked = true;
else
menuItem.Checked = false;
Your statement is actually doing a toggle effect on the menuItem. If it is Checked then the statement is setting it to UnChecked and vice versa
From MSDN ?: Operator (C# Reference)
The conditional operator (?:) returns one of two values depending on
the value of a Boolean expression. Following is the syntax for the
conditional operator.m
condition ? first_expression : second_expression;

This can be replaced with following code:
menuItem.Checked = !menuItem.Checked;

That's the equivalent of :
menuItem.Checked = !menuItem.Checked;

Here is the MSDN article on it. It has links to other useful operators: http://msdn.microsoft.com/en-us/library/ty67wk28.aspx

It's called Ternary Operators and a simple Google search gives great information about how this works and possibilities.
Take a look: https://www.google.com/search?q=Ternary+Operators+c%23
As people already have pointed out, this is just a shorter and easier way to write simple if-statements.

It is called a ternary operator. It is used like an if else statement but more condensed.
Its called ternary because it takes three operands.
It evaluates the first, and then choses the second if true, third if false.

Inline conditional c# - next best solution?

It seems the compiler is not going let this syntax fly.
void main()
{
foo(false?0:"");
}
void foo(int i) {return;}
void foo(string s) {return;}
The only other way I can see of fixing this is something as follows:
void bar(object o)
{
if (o is string){//do this}
else{//im an int, do this}
}
Anyone have any better ideas?

You cannot use a method with a void return type in a ternary expression in this way. End of story.
To understand why this is, remember what the ternary operator actually does -- it evaluates to the following:
(condition ? [true value] : [false value])
What this implies is that the following code:
int x = a ? b : c;
Must be rewritable to:
int x;
if (a)
{
x = b;
}
else
{
x = c;
}
The two above are logically identical.
So how would this work with a method with void as its return type?
// Does this make sense?
int x = condition ? foo(s) : foo(i);
// Or this?
if (condition)
{
x = foo(s);
}
else
{
x = foo(i);
}
Clearly, the above is not legal.
That said, others' suggestions would otherwise be valid if only your foo overloads returned a value.
In other words, if your signatures looked like this:
object foo(string s);
object foo(int i);
Then you could do this (you're throwing away the return value, but at least it'll compile):
object o = condition ? foo(0) : foo("");
Anyway, the ol' if/else is your best bet, in this case.

The method call of foo is determined at compile time, so it cannot call a different method (or overload) based on the result of evaluating the condition. Instead, try something like this:
condition ? foo(0) : foo("")
This way, the compiler will succeed in performing overload resolution and will resolve the first call to foo(int) and the second call to foo(string).
EDIT: As noted by other, you cannot use the ?: operator as a statement, nor can you use methods which return void in it. If your actual methods return compatible types, you could do something like:
int result = condition ? foo(0) : foo("");
If not, you must use an if:
if (condition)
foo(0);
else
foo("");

You're example doesn't make a whole lot of sense (the second example doesn't relate to the first).
I think the first example would be fine as:
void main()
{
foo("");
}
Since 0 will never be passed anyway (false is always false) and you can't use the inline conditional operator without an assignment somewhere (which your example is lacking).
As for the second way, that is probably how I would prefer to see it:
void bar(object o)
{
if(o is string) foo(o as string);
else foo((int)o);
}

I wouldn't pass in an object as a parameter. The int will be boxed, which is a little less efficient. Let the compiler figure out which method to call.
If you wrote:
foo(0);
foo("");
The appropriate method would be called. You could also write:
if (condition) {
foo(0);
} else {
foo("");
}
Depending on what you're trying to do (your example is lacking in a little detail).

If you use Inline if expressions in C#, both parts before and after the ":" have to be of the same type. What you are intending would never work.
Even if you like to do something like this:
DateTime? theTime = true ? DateTime.Now : null;
The compiler is not satisfied. In this case you will have to use:
DateTime? theTime = true ? DateTime.Now : default(DateTime?);

The conditional operator needs the true and false part to be of the same type. Which is why it's not compiling.
var x = condition ? 0 : "";
What type should the compiler choose for x? If you really want it to choose object make a cast or you could force it to choose dynamic in which case method overload would still work but you loose type safety. Both are however strong smells.
Having to test the runtime type is usually a design error but with the limited code (that will always have the same result) it's hard to help with a different approach that would require testing on runtime types

This:
foo(false?0:"")
Could be this:
false ? foo(0) : foo("")

Both results of the conditional operator must of the same type (or be implicitly convertible). So foo(false ? 0 : "") won't work because it is trying to return an Int32 and a String. Here's more information on the conditional operator.
The fix I would do is change that line to false ? foo(0) : foo("").
EDIT: Derp, can't use a conditional operator just in the open like that. They can only be used for assignments. You'll have to use a if/else block. Not in one line, but it'll do in a pinch.