find if an integer exists in a list of integers

Question

i have this code     List lt T gt  apps   getApps             List lt int gt  ids           List lt SelectListItem gt  dropdown   apps ConvertAll c   gt  new SelectListItem                       Selected   ids Contains c Id               Text   c Name              Value   c Id ToString              ToList      ids Contains   seems to always return false even though the numbers do match  any ideas

User · Answer

The way you did is correct  It works fine with that code  x is true  probably you made a mistake somewhere else   List lt int gt  ints   new List lt int gt   new    1 5 7       1     List lt int gt  intlist new List lt int gt      0 2 3 4 1      2     var i   5  var x   ints Contains i        return true or false

User · Answer

bool vExist   false  int vSelectValue   1   List lt int gt  vList   new List lt int gt     vList Add 1   vList Add 2    IEnumerable vRes    from n in vListwhere n    vSelectValue   if  vRes Count  gt  0        vExist   true

User · Answer

If you just need a true false result  bool isInList   intList IndexOf intVariable     -1    if the intVariable does not exist in the List it will return -1

User · Answer

string name   abc   IList lt string gt  strList   new List lt string gt       abc     def    ghi    jkl    mno     if  strList Contains name       Console WriteLine  Got It                           OR                           IList lt int gt  num   new List lt int gt     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

User · Answer

The best of code and complete is here   NumbersList Exists p   gt  p Equals Input    Use   List lt int gt  NumbersList   new List lt int gt     private void button1 Click object sender  EventArgs e        int Input   Convert ToInt32 textBox1 Text       if   NumbersList Exists p   gt  p Equals Input                 NumbersList Add Input             else               MessageBox Show  The number entered is in the list   Error

User · Answer

As long as your list is initialized with values and that value actually exists in the list  then Contains should return true   I tried the following   var list   new List lt int gt   1 2 3 4 5   var intVar   4  var exists   list Contains intVar     And exists is indeed set to true

User · Answer

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

User · Answer

Here is a extension method  this allows coding like the SQL IN command   public static bool In lt T gt  this T o  params T   values        if  values    null  return false       return values Contains o     public static bool In lt T gt  this T o  IEnumerable lt T gt  values        if  values    null  return false       return values Contains o       This allows stuff like that   List lt int gt  ints   new List lt int gt   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

[c#] find if an integer exists in a list of integers

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