In addition, a narrowing primitive conversion may be used if all of the following conditions are satisfied:
The expression is a constant expression of type byte, short, char or int. The type of the variable is byte, short, or char. The value of the expression (which is known at compile time, because it is a constant expression) is representable in the type of the variable.
The first point gives ur solution.
short a=10; char c=a;
since a is not a constant expression, thats why the compiler flags an error.