Declared and undeclared global variables The mechanism for storing and accessing them is the same, but JavaScript treats them differently in some cases based on the value of the configurable attribute (described below). In regular usage, they should behave the same. Both exist in the global object Below are some comparisons of declared and undeclared … Read more
There are several ways to introduce variables. DEFVAR and DEFPARAMETER introduce global dynamic variables. DEFVAR optionally sets it to some value, unless it is already defined. DEFPARAMETER sets it always to the provided value. SETQ does not introduce a variable. (defparameter *number-of-processes* 10) (defvar *world* (make-world)) ; the world is made only once. Notice that … Read more
Why not just do this: var = None Python is dynamic, so you don’t need to declare things; they exist automatically in the first scope where they’re assigned. So, all you need is a regular old assignment statement as above. This is nice, because you’ll never end up with an uninitialized variable. But be careful … Read more
It’s syntactically valid, since the variable’s point of declaration comes before its initialiser, and the name is available anywhere after that point. This allows less dodgy initialisations like void *p = &p; which legitimately uses the name (but not the value) of the variable being initialised. It’s behaviourally invalid, since using the value of an … Read more
As of C++17 what you were trying to do is finally possible: if (int a = Func1(), b = Func2(); a && b) { // Do stuff with a and b. } Note the use of ; of instead of , to separate the declaration and the actual condition.
Stack space for local variables is usually allocated in function scope. So no stack pointer adjustment happens inside the loop, just assigning 4 to var. Therefore these two snippets have the same overhead.
This is excellent practice. By creating variables inside loops, you ensure their scope is restricted to inside the loop. It cannot be referenced nor called outside of the loop. This way: If the name of the variable is a bit “generic” (like “i”), there is no risk to mix it with another variable of same … Read more
Okay, first things first. There is no such thing as “variable declaration” or “variable initialization” in Python. There is simply what we call “assignment”, but should probably just call “naming”. Assignment means “this name on the left-hand side now refers to the result of evaluating the right-hand side, regardless of what it referred to before … Read more
The delete operator removes a property from an object. It cannot remove a variable. So the answer to the question depends on how the global variable or property is defined. (1) If it is created with var, it cannot be deleted. For example: var g_a = 1; //create with var, g_a is a variable delete … Read more
This comes in useful when you have global variables. You declare the existence of global variables in a header, so that each source file that includes the header knows about it, but you only need to “define” it once in one of your source files. To clarify, using extern int x; tells the compiler that … Read more