CODEWITHSUNDEEP
c#
der chuan
der chuan

Reputation: 13

Problem Checking Existence of Element of C# List using Contains()

List<int[]> three_number_sums = new List<int[]>();

int[] _3Ints_arr = { 2, 6, 9 };

three_number_sums.Add(_3Ints_arr); // storing array in List as 2,6,9

_3Ints_arr[0] = 1;
_3Ints_arr[1] = 10;
_3Ints_arr[2] = 100;  // array now is 1,10,100

if(!three_number_sums.Contains(_3Ints_arr))  // does not exist
    three_number_sums.Add(_3Ints_arr);

I wonder why my program under the if statement still treats as exists even after overriding _3Ints_arr with 1,10,100?

This same concept works (if treated as not exists) for List of strings however once "apple" is overridden by "orange" in the string:

List <string> words = new List <string> ();

string word = "apple";

words.Add(word);  // storing word in List as "apple"

word = "orange";  // string now is "orange"

if (!words.Contains(word))  // does not exist 
   words.Add(word);

Upvotes: 1

Views: 44

Answers (1)

Alessandro
Alessandro

Reputation: 116

In the first example, the list contains the reference to the array _3Ints_arr. When you change the content of this array, the reference to the array doesn't change and three_number_sums.Contains(_3Ints_arr) returns true.

In the second example you are using string, which is immutable: when you assign a new value to word, word is no more the reference you had added to the list. So words.Contains(word) is false.

Upvotes: 2

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