johnwong - Developer IT

virtualbox - debian with no-ip

- by JohnWong

Hi. I have VB on my XP SP3. I am running one guest OS, Debian. I installed it using the 150MB, and everything seems to work fine. I am using 3.1.6 VB The purpose of this server is running php, mysql and django project. So I need access both locally and externally. I usually do it with my no-ip. I have experience with Ubuntu server, and using noip2 was a cake. I had this "domain" xxx.no-ip.org. I need this to be use on my debian server, so that I can type xxx.no-ip.org into the firefox (on my xp). I checked ifconfig, pstree. They showed that debian grabbed the right ip (it matched with my ip), and pstree showed noip2 has already been activated (under init.d) But I can't access to xxx.no-ip.org from my windows in firefox how come? back in the days when I used ubuntu as its own installation (instead of VM), noip2 worked like a cake without any twist. Any thoughts? Thank you!

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html css header text

- by JohnWong

I am trying to move the nav text (home...) up in the middle to the right. But when I do -120px for the top (nav.li), it eats up part of the banner. How can I fix that? Thanks body { background-color: #D6E2FF; } #headerimg { margin: 10px 0px 0px 0px; height: fixed; width: 95%; } #header { height:auto; background:url("menubar.jpg") no-repeat; } #logo { background: transparent url("logo.jpg") no-repeat; display: block; width: 146px; height: 146px; border: none; } #navcontainer { font-size: 200%; margin: -100px 0px 0px 500px; } #navlist li { display: inline; list-style-type: none; padding-right: 30px; color: #FFFFFF; }

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help with array

- by JohnWong

You will write a program that evaluates the integral of sin(x) using the left-hand rectangle rule with 2000 subintervals, over 10 intervals. The intervals to test are [0, 1), [1, 2), …, [8, 9), [9, 10). You will declare an array of type double that can hold 10 elements, and you will use this array to hold all 10 results you get from evaluating each interval. I am in testing my code, what should be the output? For example, [0, 1)? Any idea? Thanks.

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array, I/O file and standard deviation (c++)

- by JohnWong

double s_deviation(double data[],int cnt, double mean) { int i; double sum= 0; double sdeviation; double x; //x = mean(billy,a_size); for(i=0; i<cnt; i++) { sum += ((data[i]) - (mean)); } sdeviation = sqrt(sum/((double)cnt)); return sdeviation; } When I cout the result from this function, it gave me NaN. I tested the value of (mean) and data[i] using return data[i] and return mean they are valid. when i replaced mean with an actual number, the operation returned a finite number. but with mean as a variable, it produced NaH. I can't see anything wrong with my code at the moment. Again, I am sure mean, data are getting the right number based on those tests. Thank you

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give feedback on this pointer program

- by JohnWong

This is relatively simple program. But I want to get some feedback about how I can improve this program (if any), for example, unnecessary statements? #include<iostream> #include<fstream> using namespace std; double Average(double*,int); int main() { ifstream inFile("data2.txt"); const int SIZE = 4; double *array = new double(SIZE); double *temp; temp = array; for (int i = 0; i < SIZE; i++) { inFile >> *array++; } cout << "Average is: " << Average(temp, SIZE) << endl; } double Average(double *pointer, int x) { double sum = 0; for (int i = 0; i < x; i++) { sum += *pointer++; } return (sum/x); } The codes are valid and the program is working fine. But I just want to hear what you guys think, since most of you have more experience than I do (well I am only a freshman ... lol) Thanks.

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reference function from another function

- by JohnWong

I forgot how to reference another function into a function in C++? In python it is declare as a class so that I can use it. double footInches(double foot) { double inches = (1.0/12.00) * foot; return inches; } double inchMeter(double inch) { double meter = 39.37 * (footInches(inches)); return meter; } I want to reference footInches in inchMeter.

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linked list problem (with insert)

- by JohnWong

The problem appears with the insert function that I wrote. 3 conditions must work, I tested b/w 1 and 2, b/w 2 and 3 and as last element, they worked. But b/w 3 and 4, it did not work. It only display up to the new added record, and did not show the fourth element. Efficiency is not my concern here (not yet). Please guide me through this debug process. Thank you very much. #include<iostream> #include<string> using namespace std; struct List // we create a structure called List { string name; string tele; List *nextAddr; }; void populate(List *); void display(List *); void insert(List *); int main() { const int MAXINPUT = 3; char ans; List * data, * current, * point; // create two pointers data = new List; current = data; for (int i = 0; i < (MAXINPUT - 1); i++) { populate(current); current->nextAddr = new List; current = current->nextAddr; } // last record we want to do it sepeartely populate(current); current->nextAddr = NULL; cout << "The current list consists of the following data records: " << endl; display(data); // now ask whether user wants to insert new record or not cout << "Do you want to add a new record (Y/N)?"; cin >> ans; if (ans == 'Y' || ans == 'y') { /* To insert b/w first and second, use point as parameter between second and third uses point->nextAddr between third and fourth uses point->nextAddr->nextAddr and insert as last element, uses current instead */ point = data; insert(()); display(data); } return 0; } void populate(List *data) { cout << "Enter a name: "; cin >> data->name; cout << "Enter a phone number: "; cin >> data->tele; return; } void display(List *content) { while (content != NULL) { cout << content->name << " " << content->tele; content = content->nextAddr; cout << endl; // we skip to next line } return; } void insert(List *last) { List * temp = last->nextAddr; //save the next address to temp last->nextAddr = new List; // now modify the address pointed to new allocation last = last->nextAddr; populate(last); last->nextAddr = temp; // now link all three together, eg 1-NEW-2 return; }

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How do I use requestFocus in a Java JFrame GUI?

- by JohnWong

I am given an assignment but I am totally new to Java (I have been programming in C++ and Python for two years). So we are doing GUI and basically we extended JFrame and added a couple fields. Say we have a field named "Text 1" and "Text 2". When user presses enter with the cursor in Text 1, move the focus to Text 2. I tried to add private JTextField textfield1() { textfield1 = new JTextField(); textfield1.setPreferredSize(new Dimension(200, 20)); textfield1.addActionListener( new ActionListener() { public void actionPerformed(ActionEvent e) { textfield1text = textfield1.getText().trim(); textfield1.setText(textfield1text); System.out.println(textfield1text); textfield1.requestFocus(); } }); return textfield1; } But that doesn't work at all. I noticed that requestFocus is not recommended, and instead one should use requestFocusWindows. But I tried that too. Upon some readings it seems like I have to do keyboard action and listener? But my teacher said it only requires 1 line...

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class T in c++ (your definition)

- by JohnWong

The one advantage of using class T in c++ is to reduce the time to redefine data types in a function, if those data types are defined in other function, for example, in int main. template <class T> void showabs(T number) { if (number < 0 ) number = -number; cout << number << endl; return 0; } int main() { int num1 = -4; float num2 = -4.23f; showabs(num1); showabs(num2); return 0; } So in this case, without class T, for each data type, we have to add its corresponding data-type condition, that is, another set of if statement for int, and another one for float. Am I correct?

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c++ projects for beginners

- by JohnWong

So I know this is a frequent question, but I still can't find a good one. It's a 3-week internship where I get to teach high school students. I would cover basic c++ first week, and start the project second week. What I need is a project that is doable (for them) in 2 weeks. It is interesting. Somehow I want it to be interactive (something that's cool, something that we get to use a lot or something like that)? Any idea?

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