'signed' and 'unsigned' on their own--act as short-hand for 'signed int' and 'unsigned int' in C and C++.
Note that the size of an 'int' is dependant on the "data model"[1]. As for whether it's the most optimal is far too context dependant.
A data model that defaults 'int's to 32 bits on today's (and yesterday's) architectures is fine in many cases as the range of that type is acceptable for most usages without excessive wastage.
Certain data models do specify that 'int' is 64 bits which can break some programmer's assumptions, and also lead to space wastage as a struct member or a stack slot has to have 64 bits allocated for it on paper.
Data models are part of the ABI your program uses, so it's not necessarily optimal for any given system.
Note that the size of an 'int' is dependant on the "data model"[1]. As for whether it's the most optimal is far too context dependant.
A data model that defaults 'int's to 32 bits on today's (and yesterday's) architectures is fine in many cases as the range of that type is acceptable for most usages without excessive wastage.
Certain data models do specify that 'int' is 64 bits which can break some programmer's assumptions, and also lead to space wastage as a struct member or a stack slot has to have 64 bits allocated for it on paper.
Data models are part of the ABI your program uses, so it's not necessarily optimal for any given system.
[1] Wikipedia has a table summarizing some of the differences: https://en.wikipedia.org/wiki/64-bit_computing#64-bit_data_m...