float radius;
String msg= ("what is the raduis of your circle");
float area;
String msg2= ("your circle has area of");
float pi= 3.14;
int j;
int BT=500;
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);
}