String Find in C#

In C#, you can find the index of a substring using IndexOf():

s.IndexOf(sub)           // returns index of first occurrence, or -1 if not found
s.LastIndexOf(sub)       // returns index of last occurrence
s.IndexOf(sub, fromIdx)  // search starting from index `fromIdx`

Here are some examples:

string sentence = "Hello World";
int idx = sentence.IndexOf("World");
Console.WriteLine(idx);  // 6

Console.WriteLine(sentence.IndexOf("xyz"));  // -1  (not found)

The index returned is the position of the first character of the found substring.