Question

I am confused with this code.

string str = sample.indexof("a",0);

It’s working. But below not working.

string str = sample.indexof("\",0);

Answer 1

You need to escape backslashes in string and character literals in C# – or use a verbatim string literal. Any of these will work:

int index = sample.IndexOf("\\", 0);
int index = sample.IndexOf(@"\", 0);
int index = sample.IndexOf('\\', 0);

Or without specifying the initial index, if you’re looking from the start anyway:

int index = sample.IndexOf("\\");
int index = sample.IndexOf(@"\");
int index = sample.IndexOf('\\');

Personally I would use the last of these if you’re only looking for a single character – it’s clearer that it really is exactly one character. (It may be marginally more efficient too, but the clarity is more important.)

(Note that C# is case sensitive – it’s IndexOf, not indexof. Also note that it returns int, not string. It helps if you can make your sample code accurate…)