float radius;
String msg="What is the Radius?";
float area;
String msg2="Your area is - ";
float pi=3.14;

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

}

void loop() {
  // put your main code here, to run repeatedly:
Serial.println(msg);
while (Serial.available()==0){

}
radius=Serial.parseFloat();
area=pi*radius*radius;
Serial.print(msg2);
Serial.println(area);
}