I want to change the code I wrote using AVAudioPCMBuffer on swift to objective-C.

If you use AVAudioPCMBuffer in swift to write a value to the buffer and sound a sine wave
http://www.tmroyal.com/playing-sounds-in-swift-audioengine.html
It was made by referring to .
I'd like to write this as objective-C, but I'm having a hard time because I don't know how to send a message when I write a value on the buffer.
Here's the swift from the previous site.

for vari=0;i<Int(buffer.frameLength);i+=Int(n_channels){
        varval=sinf (441.0*Float(i)*2*Float(M_PI)/sr)

        buffer.floatChannelData.memory[i] = val * 0.5
    }

When I try to write this in objective-C, buffer.floatChannelData appears as a complement, but memory[i] does not appear as a complement.
Definitely,

 buffer.floatChannelData.memory[i]=val;

I thought I could write in , but how should I write it?

I look forward to your kind cooperation.