find if an integer exists in a list of integers

Question

i have this code:

  List apps = getApps();

        List ids;

        List dropdown = apps.ConvertAll(c => new          


        

Answer 1

The best of code and complete is here:

NumbersList.Exists(p => p.Equals(Input)

Use:

List<int> NumbersList = new List<int>();
private void button1_Click(object sender, EventArgs e)
{
    int Input = Convert.ToInt32(textBox1.Text);
    if (!NumbersList.Exists(p => p.Equals(Input)))
    {
       NumbersList.Add(Input);
    }
    else
    {
        MessageBox.Show("The number entered is in the list","Error");
    }
}

Answer 2

The way you did is correct. It works fine with that code: x is true. probably you made a mistake somewhere else.

List<int> ints = new List<int>( new[] {1,5,7}); // 1

---

List<int> intlist=new List<int>() { 0,2,3,4,1}; // 2

---

var i = 5;
var x = ints.Contains(i);   // return true or false

Answer 3

Here is a extension method, this allows coding like the SQL IN command.

public static bool In<T>(this T o, params T[] values)
{
    if (values == null) return false;

    return values.Contains(o);
}
public static bool In<T>(this T o, IEnumerable<T> values)
{
    if (values == null) return false;

    return values.Contains(o);
}

This allows stuff like that:

List<int> ints = new List<int>( new[] {1,5,7});
int i = 5;
bool isIn = i.In(ints);

Or:

int i = 5;
bool isIn = i.In(1,2,3,4,5);

Answer 4

You should be referencing Selected not ids.Contains as the last line.

I just realized this is a formatting issue, from the OP. Regardless you should be referencing the value in Selected. I recommend adding some Console.WriteLine calls to see exactly what is being printed out on each line and also what each value is.

After your update: ids is an empty list, how is this not throwing a NullReferenceException? As it was never initialized in that code block

Answer 5

bool vExist = false;
int vSelectValue = 1;

List<int> vList = new List<int>();
vList.Add(1);
vList.Add(2);

IEnumerable vRes = (from n in vListwhere n == vSelectValue);
if (vRes.Count > 0) {
    vExist = true;
}

Answer 6

string name= "abc";
IList<string> strList = new List<string>() { "abc",  "def", "ghi", "jkl", "mno" };
if (strList.Contains(name))
{
  Console.WriteLine("Got It");
}

/////////////////   OR ////////////////////////

IList<int> num = new List<int>();
num.Add(10);
num.Add(20);
num.Add(30);
num.Add(40);

Console.WriteLine(num.Count);   // to count the total numbers in the list

if(num.Contains(20)) {
    Console.WriteLine("Got It");    // if condition to find the number from list
}