Tower Defense WaveDowmCounter

Hi Guys.
I’m new to Unity so I started learning from YT tutorials. A month ago I started Tower Defense tutorial from brackeys and I think I’ve done quite good job as I added few features on my own. However I can’t figured out how to add wave down counter which will count how many waves left in scene and once next wave is spawned I want this number to go -1.
Can somebody help with this please? I wouldn’t be posting here if I wouldn’t try to search or try to do it on my own.

This will work:

int waveCounter = 40;
float waveTimer = 30.0f;

void Update(){

    waveTimer -= Time.deltaTime;
    if(waveTimer <= 0.0f){
        waveTimer = 30.0f; //reset waveTimer

        //new wave code

        waveCounter -= 1; //subtract 1 from waveCounter

        if(waveCounter == 0){
            //all waves finished