Getting the second index of a spesific character in a string when only there is two of it

Question

I need to get the index of a specific character in a string, but I need to know if it occurs twice in that string and if it is so, get the second occurrence index. I tried a few things but couldn't find the solution. Does anyone know how can it be done in .Net? Vb.net if possible.

What I am trying is explained below:

I have string like : 01298461705691703

I need to aquire the index of 17 in this string but if the string has two 17's then I need to know the index of the second one.

Answer 1

You will need to use IndexOf two times, using its overload on the second time.

string myStr = "01298461705691703";

// Find the first occurence
int index1 = myStr.IndexOf("17");
// You might want to check if index1 isn't -1

// Find the second occurrence, starting from the previous one
int index2 = myStr.IndexOf("17", index1 + 1);
// We add +1 so that it doesn't give us the same index again
// Result will be 13

See: https://learn.microsoft.com/en-us/dotnet/api/system.string.indexof

Answer 2

Start your string from first occurrence 17, something similar to

    string str = "01298461705691703";
    int i = str.IndexOf("17", s.IndexOf("17")+1);
                            //^^^^^^^^^^^^^^^^^ This will start your string from first occurrence of 17     

Syntax of indexOf

string.IndexOf(Char, Int32)

where,

• char is a unicode character to seek.

• Int32 is starting index of string

---

If you are trying to find out last occurrence of 17 in string, then you can use string.LastIndexOf() method.

    string str = "01298461705691703";
    int lastIndex = str.LastIndexOf("17");

---

POC : .Net Fiddle

Answer 3

The solution is String.LastIndexOf

Dim myStr as String = "01298461705691703"
Dim idx as Integer = myStr.LastIndexOf("17")

or in c#

string myStr = "01298461705691703";
int idx = myStr.LastIndexOf("17");