This could be useful for some people involved in FIRST robotics, but I posted it in order to get it logic-checked.

sonicRead.cc

//earlier in the program I run this to initialize the array
for (int i = 0; i < SONIC_SAMPLE * 2; i++)
	sonicRead();

//Averages and returns the inch reading of the ultrasonic sensor
//Updates sonicHotZone
SonicData robot::sonicRead()
{
	SonicData out;
	out.avg = 0;
	
	//shift sonicLog data
	sonicLog[SONIC_SAMPLE - 1] = sonicLog[SONIC_SAMPLE - 2];//shift last value
	for (int i = 1; i <= SONIC_SAMPLE - 2; i++)//shift mid values
		sonicLog[i] = sonicLog[i - 1];
	//add new 1st value
	long double localAvg = 0;
	long double localSonicLog[10];
	for (int i = 0; i < 10; i++)
	{
	    localSonicLog[i] = sonic->GetVoltage() / VOLTS_INCH;
	    localAvg += sonicData[i];
	    feed();
	}
	localAvg /= 10;
	sonicLog[0] = localAvg;
	
	//get the average of sonicLog
	for(int i = 0; i < SONIC_SAMPLE; i++)
		out.avg += sonicLog[i];
	out.avg /= SONIC_SAMPLE;
	
	//Check for hot zone
	if (out.avg >= TOO_CLOSE
		&& out.avg <= TOO_FAR)
		out.hotZone = true;
	else
		out.hotZone = false;
	
	return out;
}

sonicRead.hh

//Ultrasonic Sensor
const int TOO_FAR = 120;
const int TOO_CLOSE = 60;
const double VOLTS_INCH = 0.009765625;//5/512
const int SONIC_SAMPLE = 10;

//Package for ultrasonic sensor data
//Datatype returned by sonicRead function
struct SonicData
{
	long double avg;//average value over SONIC_SAMPLE time
	bool hotZone;//whether or not the robot is in the hot zone
	//HOT ZONE IS SET BY TOO_FAR and TOO_CLOSE
};