Why do commas not work to include strings in WriteLine?

Question

I am wondering why a '+' is needed in a scenario like this:

string name = "Rick";
Console.WriteLine("Hello, " + name);

I was under the impression that the '+' was needed to include a variable of another type, and a string could be included without one. Is this incorrect?

Further, if that is the case, then why does it simply skip the variable and not return an error in a situation like this:

string name = "Rick";
Console.WriteLine("Hello, " , name);

Thanks.

Console.WriteLine("Hello, {0}" , name); – James R. Apr 01 '16 at 20:27 — James R., Apr 01 '16 at 20:27

score 3 · Accepted Answer · answered Apr 01 '16 at 20:27

3

As far as the compiler is concerned, the second version is trying to pass a second parameter, which the WriteLine method is not overloaded for. The options you really have for this are as follows

Console.WriteLine("Hello, " + name);
Console.WriteLine($"Hello, {name}");
Console.WriteLine(String.Format("Hello, {0}", name));

answered Apr 01 '16 at 20:27

Alfie Goodacre

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`WriteLine()` does have an appropriate overload, making the call to `Format()` unnecessary – Mathias R. Jessen Apr 01 '16 at 20:33
Ah right you are, though as the OP seems to be unsure about string concatenation so it might be worth leaving it in in case he didn't know of its existence :) – Alfie Goodacre Apr 01 '16 at 20:35
Thank you. I got confused because I remember using your third example earlier but forgot about the needed {#}. – Jeremy Apr 01 '16 at 20:45

score 2 · Answer 2 · answered Apr 01 '16 at 20:26

2

C# concatenates string using operator +. So, one strings adds to another string creating third string containing first and second strings. Comma does not concatenate strings, comma separates parameters.

answered Apr 01 '16 at 20:26

Riad Baghbanli

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score 1 · Answer 3 · edited May 23 '17 at 12:31

The first Example:

string name = "Rick"; //string variable
Console.WriteLine("Hello, " + name);

the + operator is used to concatenate the value of string variable name and the string literal "Hello, ".

The resulting output will be Hello, Rick

For more see:String Concatenation

The second example:

string name = "Rick";
Console.WriteLine("Hello, " , name);

Matches the overload Console.WriteLine(String, Object)

It requires the use of a formatter {0} because the formatter is not present nothing will happen with the second argument Object (in your case in the variable name). A proper version of this would be written as :

string name = "Rick"; Console.WriteLine("Hello, {0}", name);

The object is cast to string and creates a new string with the value of name replacing the {0} value.
The resulting output that is written to screen would be:Hello, Rick

For more info I'd recommend you look at the following:

Console.WriteLine(String, Object)

String Concatenation

On String Formatters

Literals vs Variables