First of all, I assume that you know that 6.2f * 10 is not exactly 62 due to floating point rounding (it’s actually the value 61.99999809265137 when expressed as a double) and that your question is only about why two seemingly identical computations result in the wrong value. The answer is that in the case … Read more
Expressions only contain identifiers, literals and operators, where operators include arithmetic and boolean operators, the function call operator () the subscription operator [] and similar, and can be reduced to some kind of “value”, which can be any Python object. Examples: 3 + 5 map(lambda x: x*x, range(10)) [a.x for a in some_iterable] yield 7 … Read more
You can pass it to a BeanShell bsh.Interpreter, something like this: Interpreter interpreter = new Interpreter(); interpreter.eval(“result = 5+4*(7-15)”); System.out.println(interpreter.get(“result”)); You’ll want to ensure the string you evaluate is from a trusted source and the usual precautions but otherwise it’ll work straight off. If you want to go a more complicated (but safer) approach you … Read more
This is not standard C. It is a gcc extension called statement expressions. You can find the complete list of C extensions here. This is actually one of the many gcc extensions used in the Linux kernel and it seems like clang supports this too and although it is not explicitly named in the document. … Read more
Expression: Something which evaluates to a value. Example: 1+2/x Statement: A line of code which does something. Example: GOTO 100 In the earliest general-purpose programming languages, like FORTRAN, the distinction was crystal-clear. In FORTRAN, a statement was one unit of execution, a thing that you did. The only reason it wasn’t called a “line” was … Read more
There is no difference in performance. However, the first style is ANSI-89 and will get your legs broken in some shops. Including mine. The second style is ANSI-92 and is much clearer. Examples: Which is the JOIN, which is the filter? FROM T1,T2,T3…. WHERE T1.ID = T2.ID AND T1.foo = ‘bar’ AND T2.fish = 42 … Read more
Well, you can use Expression.AndAlso / OrElse etc to combine logical expressions, but the problem is the parameters; are you working with the same ParameterExpression in expr1 and expr2? If so, it is easier: var body = Expression.AndAlso(expr1.Body, expr2.Body); var lambda = Expression.Lambda<Func<T,bool>>(body, expr1.Parameters[0]); This also works well to negate a single operation: static Expression<Func<T, … Read more
I guess this document might serve as a not so short introduction : n3055 The whole massacre began with the move semantics. Once we have expressions that can be moved and not copied, suddenly easy to grasp rules demanded distinction between expressions that can be moved, and in which direction. From what I guess based … Read more
482/10/5/2.0*2+14/5 48/5/2.0*2+14/5 9/2.0*2+14/5 4.5*2+14/5 9.0+14/5 9.0+2 11.0 Divisions go from left to right, addition comes last. An integer is only converted to double in an arithmetic operation with a double. That only happens three times: In step 3 (9/2.0), step 4 (4.5*2) and step 6 (9.0+2). All other operations are pure integer operations.
Yes, this works. For a list of all possible expressions see http://msdn.microsoft.com/en-us/library/system.data.datacolumn.expression.aspx Here also is a sample program demonstrating this works. using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Data; namespace ConsoleApplication2 { class Program { static void Main(string[] args) { DataTable table = new DataTable(); // Create the first column. DataColumn textColumn = … Read more