Question

Which of these will achieve the correct result:

(1)

int X = 23;
string str = "HELLO" + X.ToString() + "WORLD";

(2)

int X = 23;
string str = "HELLO" + X + "WORLD";

(3)

int X = 23;
string str = "HELLO" + (string)X + "WORLD";

EDIT: The ‘correct’ result is for str to evaluate to: HELLO23WORLD

Answer 1

Option 3 doesn’t compile cause you cannot cast an int to string.

The two others produce the same result. However, there’s a subtle difference.

Internally the plus operator compiles to a call to String.Concat. Concat has different overloads. Option 1 calls Concat(string, string, string) while option 2 calls Concat(object, object, object) with two strings and a boxed int. Internally Concat then calls ToString on the boxed int.

Also, check this related question: Strings and ints, implicit and explicit