variables

问题 This question already has answers here : Are python variables pointers? or else what are they? (9 answers) Closed 8 months ago . I don't understand why the variable 'y' doesn't update when I change the x? (The 'y' variable is dependent on 'x' right?) x = 5 y = x*2 print(x) print(y) x = 3 # Expect it to print '3' and '6' instead it print '3' and '10' print(x) print(y) 回答1: (The 'y' variable is dependent on 'x' right? No. Few programming languages have dependent / computed variables [0] and

问题 This question already has answers here : How do I use extern to share variables between source files? (17 answers) Closed 7 years ago . I'm writing little student project and stuck with the problem that I have a few global variables and need to use it in a few source files, but I get the error *undefined reference to variable_name*. Let's create three source files for example: tst1.h: extern int global_a; void Init(); tst1.cpp: #include "tst1.h" void Init(){ global_a = 1; } tst2.cpp: #include

问题 This question already has answers here : How do I use extern to share variables between source files? (17 answers) Closed 7 years ago . I'm writing little student project and stuck with the problem that I have a few global variables and need to use it in a few source files, but I get the error *undefined reference to variable_name*. Let's create three source files for example: tst1.h: extern int global_a; void Init(); tst1.cpp: #include "tst1.h" void Init(){ global_a = 1; } tst2.cpp: #include

问题 I'm trying to find an easy way to perform multiple null checks/ replacements in multiple variables in Java. I have an object with about 20 String variables. In the constructor I want to check if any of the variable values are null. If they are null I want to replace them with an empty String. I could perform a series of if statements but I feel like there must be a cleaner way to do this. 回答1: Unless you want to resort to reflection (which I strongly discourage) your best bet is probably to

问题 I used to "tie" my data to the DOM until I've discovered the data binding libraries. My question, say I have a table which contains model records, how can I build that table with JS, i.e pass the objects into javascript rather then straight build the table in template? so far from searching the only way I've found is things like this: var data = '{{data}}'; {{data}} could be json for this example. which seems ugly and bad to me, to put template code in javascript, and also I don't like the

问题 I used to "tie" my data to the DOM until I've discovered the data binding libraries. My question, say I have a table which contains model records, how can I build that table with JS, i.e pass the objects into javascript rather then straight build the table in template? so far from searching the only way I've found is things like this: var data = '{{data}}'; {{data}} could be json for this example. which seems ugly and bad to me, to put template code in javascript, and also I don't like the

问题 Part 1 Given this example: var number = 10 { var number = 42 } console.log(number) // 42 Why does line 4 not throw an Uncaught SyntaxError: Identifier 'number' has already been declared ? It works with let / const because of block scoping (although the output is, of course, 10 not 42 ), but how come it works with var ? Part 2 Compare this to the following, which works with var : var number = 10 var number = 42 console.log(number) // 42 but doesn't with let : let number = 10 let number = 42 //

问题 I'm trying to export the connection from mongoUtil.js to my server.js file, which worked. However, I'm also trying to export the variable collection through the function getDb() to another file where I handle a bunch of post requests, however, it says it's undefined. I've been racking my brain to understand what I'm doing incorrectly. What am I missing? mongoUtil.js const express = require('express'); const MongoClient = require('mongodb').MongoClient; var collection; module.exports = {

问题 How would I define multiple values of the same type in an array using #define ? For instance, I would like #define DIGIT 0x30 | 0x31 | 0x32 | 0x33 | 0x34 | 0x35 | 0x36 | 0x37 | 0x38 | 0x39 #define QUOTE 0x22 | 0x27 ETC... 回答1: How would I define multiple values of the same type in an array using #define ? For instance, I would like #define DIGIT 0x30 | 0x31 | 0x32 | 0x33 | 0x34 | 0x35 | 0x36 | 0x37 | 0x38 | 0x39 #define QUOTE 0x22 | 0x27 Well, the term array in C and C++ refers to a number of

问题 I'm trying to export the connection from mongoUtil.js to my server.js file, which worked. However, I'm also trying to export the variable collection through the function getDb() to another file where I handle a bunch of post requests, however, it says it's undefined. I've been racking my brain to understand what I'm doing incorrectly. What am I missing? mongoUtil.js const express = require('express'); const MongoClient = require('mongodb').MongoClient; var collection; module.exports = {