How can I store a 13 digits int in Arduino?
For example, current timestamp is: 1500666822235
An uint32_t can only hold 10 digits max.
64 bits integer does not seem to be supported on RFduino.
That 20 digits. It is the maximum value of a
uint64_t. Even the Arduino Uno can use the
uint64_t. Perhaps the
Serial.print does not support it, but the compiler supports it.
Which processor does your RFduino have ?
Where does the timestamp come from ? Perhaps you are asking the wrong question. Perhaps this is a xy-problem.