How to use two Sonar's
Maybe this one, I'll try this when I will get my second sonar


Ding ding ding! Yeah, this would be one way to do that. That creates an array so you can reference the sonar with sonar[i], where i is either 0 or 1 for the first or second number.

For only two sensors, it might be easier just to do something like this:

NewPing sonar1(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE);
NewPing sonar2(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE);


Then you can run the other code like this:

delay(100); 
unsigned int uS1 = sonar1.ping(); 
int cm1 = uS1 / US_ROUNDTRIP_CM; 

unsigned int uS2 = sonar2.ping(); 
int cm2 = uS2 / US_ROUNDTRIP_CM;


A little less code to read, whichever one you want.

The reason you can do this is you can replace the sonar with whatever you wanted (following C++ variable rules like no spaces, etc.). You could call it Arduino_Sonar if you wanted to. 

The array is basically a simple way of grouping variables together easily. It's not convenient to declare 500 differently name variables; I can just do int numbers[500]; to declare them. An array might be more useful if you're expanding your circuit, but either is correct.