String a="";
void setup() {

  Serial.begin(9600);
  // put your setup code here, to run once:

}

void loop() {
  while(a==""){
  a=Serial.readString();
  }
  
  if (a.indexOf("hello")>=0){
    Serial.println("hello whats your name?");
  }
  if (a.indexOf("ahmed")>=0){
    Serial.println("hello ahmed nice to meet you \nmy name is comp tell me how old are you");
  }
  if (a.indexOf("years")>=0){
    Serial.println("very nice");
  }

  a="";
  // put your main code here, to run repeatedly:

}