Where could I find all the C++ decimal type indicator?

This indicator you refer to is called a suffix.

For integer types, there are two types of suffixes:

1. unsigned-suffix — the character u or the character U
2. long-suffix — the character l or the character L or the long-long-suffix — the character sequence ll or the character sequence LL.

For integer literals, you can combine these suffixes, such as ul or ull to achieve both "unsignednes" and "longness" in the same literal.

There are also suffixes for floating point types: one of f, F, l, or L

1. Without suffix a literal defines double
2. f or F defines float
3. l or L defines long double

There are also user-defined literals, for which you can introduce user-defined suffixes.

As for your second question about unsigned short: there is no explicit suffix for short, so you will have to use static_cast or C-style cast.

Another way to do it is to define a user-defined literal operator like this

unsigned short operator "" _ush(unsigned long long int a)
{
    return static_cast<unsigned short>(a);
}

And then use it to define literals like this: unsigned short a = 123_ush;

I've checked that it works using this snippet:

#include <iostream>
#include <string>
#include <typeinfo>

unsigned short operator "" _ush(unsigned long long int a)
{
    return static_cast<unsigned short>(a);
}

int main()
{
  std::string name;
  bool equal = typeid(decltype(123_ush)) == typeid(unsigned short); // check that literal is indeed unsigned short
  std::cout << equal;
}

For more info on things mentioned in my answer, I would suggest checking out cppreference: Integer literals, Floating point literal, User-defined literal

You can't. There is no such thing as an unsigned short or short literal in C++.

You need to use a static_cast.

Reference: https://en.cppreference.com/w/cpp/language/integer_literal