CODEWITHSUNDEEP
c#
Sophia Antipolis
Sophia Antipolis

Reputation: 428

Unexpected behavior of ternary operator in C#

static void test(bool b)
{
    int i = 1; char c = (char)65;
    string s; if (b) s = "blubb" + i; else s = "blubb" + c;
    string t = "blubb" + (b ? i : c);
    Console.WriteLine(s + " == " + t);
}

The call test(true) gives "blubb1 == blubb1".

The call test(false) gives "blubbA == blubb65".

Additional Question

Edited:

static void test(bool b)
{
    int i = 1; char c = (char)65;
    string s; if (b) s = "blubb" + i; else s = "blubb" + c;
    string t = "blubb" + (b ? i : c);
    string u = "blubb" + (b ? c : i);
    Console.WriteLine(s + " == " + t + " == " + u);
}

The call test(true) gives "blubb1 == blubb1 == blubb65".

The call test(false) gives "blubbA == blubb65 == blubb1".

What explains this unexpected behavior?

Upvotes: 2

Views: 86

Answers (2)

Ashley Medway
Ashley Medway

Reputation: 7309

This is the key line

string t = "blubb" + (b ? i : c);

As i is of type int it casts c to an int.

The line before string s; if (b) s = "blubb" + i; else s = "blubb" + c; can be rewritten in a more readable way.

string s;
if(b)
{
    s = "blubb" + i; // i is an int here
    // So s = "blubb" + 1;
}
else
{
    s = "blubb" + c; // c is a char here. The char 'A'.
    // So s = "blubb" + 'A';
}

Two answer the second part of your question. (b ? c : i) is resolving to an int when you would expect to see a char.

This is because converting a char to an int is an implicit conversion.
Where as converting an int to a char is a explicit conversion.

In the ternary operator the implicit conversion is used.

Upvotes: 2

dav_i
dav_i

Reputation: 28157

From MSDN:

condition ? first_expression : second_expression
...
Either the type of first_expression and second_expression must be the same, or an implicit conversion must exist from one type to the other.

As there is an explicit conversion between char and int (but only an explicit the other way around) the type of the following call

boolean ? integer : character

is int.

When you concatenate any non-string object with a string, ToString() is called on the object.

This means:

  "string" + integer
= "string" + integer.ToString()

and

  "string" + character
= "string" + character.ToString()

and finally

  "string" + (boolean ? integer : character)
= "string" + integerResult
= "string" + integerResult.ToString()

Upvotes: 2

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