int arr; and I need to send it through Serial. But I don't know how to do it. is it possible?
In the comment you write that the receiving end is an Arduino too. Then you can send the data in binary form.
To send the array:
Serial.write((byte*) arr, sizeof(arr));
(byte*)is cast of the memory location of arr to a byte array
sizeofreturns the size of the array in bytes
To receive the binary data you must know the size. Here we read 100 16-bit integers:
Serial.readBytes((byte*) arr, 100 * sizeof(short));
Function readBytes is one of the 'timed' functions of Stream. It waits for the next byte (until timeout).
If one Arduino is 8-bit and the second is 32-bit, then use the type
short instead of int, because the size of type int is different, but the type short is 16 bit long on all Arduinos.