void setup(){
  Serial.begin(9600);
}

void loop(){
  Serial.println("Send any number 0-3 digits");
  getInput();
}

int getInput(){
   int serAva;                           // i is a counter, serAva hold number of serial available
   char inByte;
   char inputBytes [4]={'\0','\0','\0','\0'};                 // Array hold input bytes

   while ((serAva=Serial.available()) <= 0) {  //set serAva to how many bytes are available and wait until data arrives
    delay(50);
   }
   Serial.print("Bytes available: ");
   Serial.println(serAva);
   for(int i=0;i<serAva;i++){                  //itterate through all the bytes present
     inputBytes[i]=Serial.read();              //Store the byte into array
     Serial.println(inputBytes);             //debug for varification
   }
   return atoi(inputBytes);    // Call atoi function and return result
}