String find

[undph]

Im writing a calculator. I want to include a sinus-function.

  for(int i = 0; i < anzahlOperanden; i++){
		if (zahlen.at(i) == "PI"){
		zahlen.at(i) = "3.14159";
		}

		string umwandeln = zahlen.at(i);
		int sinStelle = umwandeln.find("sin(");

So I know that a if-function has to follow. But what does the string.find(); function return when the sub-string is not in the string?

[Smac89]

std::string::find

Return value:
The position of the first character of the first match.
If no matches were found, the function returns string::npos.

std::string::npos
http://www.cplusplus.com/reference/string/string/npos/

In short, it returns -1 when a match is not found