string result = str.Substring(0,5);
string str = "youtube";
char firstCharacter = str[0];
string str = "ararara";
string str1 = str.Substring(0,1); // returns string so [a ]
char str2 = str[0]; // This uses the String.Chars indexer, returns 'a'
char str3 = str.First(); // returns first character 'a' same as [0]
Console.WriteLine("str.Substring(0,1) {0}
str[0] {1}
str.FirstOrDefault() {2}", str1,str2,str3);
//get the 4 characters from the List of string
// first convert the list into a string
string result = string.Join("", lstData.ToArray());
// now you can use the substring function
var finalResult = result.Substring(0, 4);