'incomingData' can not be used as a function

I used this Ok a few years ago, now tried it again but get this error. This could be an old code that I messed with and now the error, but can not now see what the heck I have done wrong.
I take an ASCII code via serial port from RoboRealm and use this to track an object. well I did… :o

Any guidance/ help would be appreciated as I am a newbie on Arduino from moving over from Picaxe.
Cheers in anticipation…

#include <Servo.h> // Include the servo library

Servo myServo;//Create a new servo object

char incomingData[4]={0,0,0,0}; //A buffer to store the ASCII value read in from the serial port
int distance=0; //The distance of the object from the centre of the screen
int currentAngle=90; //The current angle of the servo
int i=0;//counter

void setup() {
  Serial.begin(9600);//open the serial port with a 9600 baud rate
  Serial.print("Serial port ready");
  myServo.attach(9);//Attach the servo signal line to pin 9
  myServo.write(currentAngle); //Set the start angle at 90 degrees
  
}

void loop()
{
  // Wait for data to become available at serial port
  if (Serial.available()){
  //Get the data coming through the serial port and store it in the buffer
  
  while (i<4){
    incomingData(i)=Serial.read(); // assign the input value to the incomingData buffer
    i++;//increment the counter
  }

  distance=atoi(incomingData); //Convert ASCII to Int

  //If the distance is negative then add 1 to the currentAngle and update the servo, and visa versa. Allow
  //the object to be within 15px of the centre without moving the servo.
  if (distance < -15){
    currentAngle++;
    currentAngle=constrain(currentAngle, 0, 180); //Constrain the value of the currentAngle to within 0 - 180 degrees
    myServo.write(currentAngle);
    }
  //Serial.printIn(currentAngle);// For debugging
  }

  i=0; //reset counter
  delay(50); //delay 20ms to allow servo to rotate to new position.
  
  }
incomingData(i)=Serial.read();

I think you meant.

incomingData[i]=Serial.read();

SpecSavers comes to mind.....Thanks a bunch, I have looked so much I have got blind...doh!
much appreciated.
I am having loads of trouble with my syntax, I have used Picaxe for years and now seen the light, just got to bring my brain up to speed... :confused: