Detect a specific frequency tone

[Lukezzz]

I have a general question. Is it possible to write a C++ program that can detect specific frequency tones, like 1 Mhz, 2Mhz 3Mhz etc...
Until now I have written standard code in C++ both native and mangaged and can manage the most components etc.. so I have a very good start.
Is this very different and could this be seen as much more difficult.
What could be my start to do this.

The goal is simply this: To detect a single frequence tone and then some simple code will execute.

[MosaicFuneral]

What type of input, and what sort of format is it in?

[Ezzaral]

An FFT would isolate it very easily. There a a lot of implementations already available in C++.

[Lukezzz]

I would have a mp3 file on the computer that a program will access and play. The signal will be a single frequency tone.

I wonder if I need to output this signal trough the LineOut of the computer and then to LineIn again or is it possible to detect the sound directly internally.

I am reading about the FFT now. It seems quite difficult but are not sure yet.

An FFT would isolate it very easily. There a a lot of implementations already available in C++.