cannot read the data from arduino to the c#

Using Arduino Interfacing w/ Software on the Computer
29

Simple serial monitor test code that sends back what is sent to the arduino. If this works, then the issue is with your pc code. If your pc code opens/closes the pc com port on each write, that will cause the arduino to reset each write.

// zoomkat 7-30-11 serial I/O string test
// type a string in serial monitor. then send or enter
// for IDE 0019 and later

String readString;

void setup() {
  Serial.begin(9600);
  Serial.println("serial test 0021"); // so I can keep track of what is loaded
}

void loop() {

  while (Serial.available()) {
    delay(2);  //delay to allow byte to arrive in input buffer
    char c = Serial.read();
    readString += c;
  }

  if (readString.length() >0) {
    Serial.println(readString);

    readString="";
  } 
}