problem taking delay out of ping code

hey all,
i'm trying replace delay in ping sensor example code timer delay can have other things running @ same time.
i getting hung in attempts , new this. here code have far

code: [select]

/* ping))) sensor
 
   this sketch reads ping))) ultrasonic rangefinder , returns the
   distance closest object in range. this, sends pulse
   to sensor initiate reading, listens pulse
   to return.  length of returning pulse proportional
   the distance of object sensor.
     
   the circuit:
* +v connection of ping))) attached +5v
* gnd connection of ping))) attached ground
* sig connection of ping))) attached digital pin 7

   http://www.arduino.cc/en/tutorial/ping
   
   created 3 nov 2008
   by david a. mellis
   modified 30 aug 2011
   by tom igoe

   this example code in public domain.

*/

// constant won't change.  it's pin number
// of sensor's output:
const int pingpin = 7;

//timer
long previousepingtimer = 0;
long pingpausetwo = 2;
long pingpausefive = 5;
long pingpauselong = 100;
long initialtimer=0

void setup() {
  // initialize serial communication:
  serial.begin(9600);
}

void loop()
{
unsigned long currentmillis = millis();            //start timer


  // establish variables duration of ping,
  // , distance result in inches , centimeters:
  long duration, inches, cm;

  // ping))) triggered high pulse of 2 or more microseconds.
  // give short low pulse beforehand ensure clean high pulse:
   
  pinmode(pingpin, output);
if(currentmillis - previousepingtimer = initialtimer)
{
  digitalwrite(pingpin, low);
} 
   if(currentmillis - previousepingtimer = pingpausetwo)
  {
  digitalwrite(pingpin, high);
  }
   if(currentmillis - previousepingtimer - pingpausetwo = pingpausefive)
   {
  digitalwrite(pingpin, low);
   

  // same pin used read signal ping))): high
  // pulse duration time (in microseconds) sending
  // of ping reception of echo off of object.
  pinmode(pingpin, input);
  duration = pulsein(pingpin, high);

  // convert time distance
  inches = microsecondstoinches(duration);
  cm = microsecondstocentimeters(duration);
 
  serial.print(inches);
  serial.print("in, ");
  serial.print(cm);
  serial.print("cm");
  serial.println();
   }
   
  if(currentmillis - previousepingtimer - pingpausetwo - pingpausefive = pingpauselong)
  {
    previousepingtimer = currentmillis;
  }
}

long microsecondstoinches(long microseconds)
{
  // according parallax's datasheet ping))), there are
  // 73.746 microseconds per inch (i.e. sound travels @ 1130 feet per
  // second).  gives distance travelled ping, outbound
  // , return, divide 2 distance of obstacle.
  // see: http://www.parallax.com/dl/docs/prod/acc/28015-ping-v1.3.pdf
  return microseconds / 74 / 2;
}

long microsecondstocentimeters(long microseconds)
{
  // speed of sound 340 m/s or 29 microseconds per centimeter.
  // ping travels out , back, find distance of the
  // object take half of distance travelled.
  return microseconds / 29 / 2;
}

i getting error
sketch_jun02b:28: error: expected unqualified-id before numeric constant
sketch_jun02b:36: error: expected ',' or ';' before 'void'
sketch_jun02b.ino: in function 'void loop()':
sketch_jun02b:54: error: lvalue required left operand of assignment
sketch_jun02b:58: error: lvalue required left operand of assignment
sketch_jun02b:62: error: lvalue required left operand of assignment
sketch_jun02b:84: error: lvalue required left operand of assignment

any appreciated. thanks

if(currentmillis - previousepingtimer = initialtimer) >>>>>>> if(currentmillis - previousepingtimer == initialtimer)

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