c# - Get the index of Array List -

i have question array list in c#

i have array following elements:

- lqi request - 0123456 - lqi request - 456789 - lqi request - 6789 ..... 

now want is, find strings lqi request, , string next it, that's i've tried far:(index global variable)

if(mystring.contains("lqi"))             {                 index= stored_data.indexof(mystring);             } messagebox.show(index.tostring()); messagebox.show(stored_data[index+1].tostring()); 

verytime run code, index stays same. should be: 0,2,4

please help

list<string> data = new list<string> {     "- lqi request",     "- 0123456",     "- lqi request",     "- 456789",     "- lqi request",     "- 6789" };  var result = data.select((x, i) => // x element, index                         {                             if (x.contains("lqi"))                                 if(i + 1 < data.count) // index inside bounds of array                                     return data[i + 1].substring(2); // don't take "- "                             return string.empty;                         }).where(x => !string.isnullorempty(x)) // ignore empty results                           .toarray();  // result: ["0123456", "456789", "6789"]