Is there a function to convert degrees into radians in C++?

I have to make a program in DevC++ and the teacher told us that there is a C++ function that does the conversion, but after lots and lots of searching I couldn't find such thing. I used radian = PI * degree / 180 , but he told us to use that specific function, which we have to find for ourselves. Any ideas what he was talking about? Is he making a mistake?