The hardest problem I’ve come across is shuffling a list. The Fisher-Yates algorithm (also sometimes known as the Knuth algorithm) involves iterating through the list swapping each item with a random other item. The algorithm is O(n), well known and long-since proven correct (an important property in some applications). But it requires mutable arrays. That … Read more
Because StatefulWidget inherits Widget, which is marked as @immutable, any subclass of StatefulWidget must also be immutable (i.e. all fields final). If you make a StatefulWidget subclass with non-final fields, it will result in this Dart analysis warning: info: This class inherits from a class marked as @immutable, and therefore should be immutable (all instance … Read more
This is because of the way Python resolves names with the .. When you write self.list the Python runtime tries to resolve the list name first by looking for it in the instance object, and if it is not found there, then in the class instance. Let’s look into it step by step self.list.append(1) Is … Read more
Quite simply, JavaScript variables do not have types. The values have types. The language permits us to write code like this: var foo = 42; foo = ‘the answer’; foo = function () {}; So it would be pointless to specify the type in a variable declaration, because the type is dictated by the variable’s … Read more
Doing a = 28 (with a being an int) is an atomic operation. But doing a++ is not an atomic operation because it requires a read of the value of a, an incrementation, and a write to a of the result. As a result, if you used a++ to implement a thread-safe counter, you could … Read more
There are multiple ways to do this. You can use a sub query: SET @some_var = (SELECT COUNT(*) FROM mytable); (like your original, just add parenthesis around the query) or use the SELECT INTO syntax to assign multiple values: SELECT COUNT(*), MAX(col) INTO @some_var, @some_other_var FROM tab; The sub query syntax is slightly faster (I … Read more
Your problem stems from a misunderstanding of the or operator that is common to people learning programming languages like this. Yes, your immediate problem can be solved by writing x ~= 0 and x ~= 1, but I’ll go into a little more detail about why your attempted solution doesn’t work. When you read x … Read more
Only x is a pointer to int; y and z are regular ints. This is one aspect of C declaration syntax that trips some people up. C uses the concept of a declarator, which introduces the name of the thing being declared along with additional type information not provided by the type specifier. In the … Read more
jQuery is just a javascript library that makes some extra stuff available when writing javascript – so there is no reason to use jQuery for declaring variables. Use “regular” javascript: var name = document.myForm.txtname.value; alert(name); EDIT: As Canavar points out in his example, it is also possible to use jQuery to get the form value: … Read more
SELECT salary INTO @variable1 FROM employee_info WHERE emp_id = 12345678 LIMIT 1; or SET @variable1 = (SELECT salary FROM employee_info WHERE emp_id = 12345678 LIMIT 1); SELECT @variable1;