Correct me if I am wrong,
int is 4 bytes, with a range of values from -2,147,483,648 to 2,147,483,647 (2^31)
long is 4 bytes, with a range of values from -2,147,483,648 to 2,147,483,647 (2^31)
What is the difference in C++? Can they be used interchangeably?
It is implementation dependent.
For example, under Windows they are the same, but for example on Alpha systems a long was 64 bits whereas an int was 32 bits. This article covers the rules for the Intel C++ compiler on variable platforms. To summarize:
OS arch size Windows IA-32 4 bytes Windows Intel 64 4 bytes Windows IA-64 4 bytes Linux IA-32 4 bytes Linux Intel 64 8 bytes Linux IA-64 8 bytes Mac OS X IA-32 4 bytes Mac OS X Intel 64 8 bytes