"do while problem"

[SneakyPeterson]

Something else just came to mind. For your program, I was assuming that you did it earlier, but did you make sure to include

#include <time.h>

#include <time.h>

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to your includes and

srand(time(0));

srand(time(0));

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to the beginning of your code execution? If you do not initialize your random number seed, then you will be generating
the same random numbers every time your code executes.

[Hardstyle]

#include<stdlib.h>
#include<qmessagebox.h>
#include<time.h>
void MainWindow::ButtonHandler()
        {
    int math[20][20];
    for (int row = 1; row < 20; row++) {
        for (int col = 1; col < 20; col++) {
            math[row][col]=0;}}
    int aux2=0;
    int aux3=0;
        srand(time(NULL));
        for(int i=0;i<100;i++)
{
bool set = false;
while(!set)
{
aux2=int( rand()%20);
aux3=int( rand()%20);
if(math[aux2][aux3]==0)
{
math[aux2][aux3] = 1;
set = true;
}
}
 
}
 int demonstration=0;
 for (int row = 1; row < 20; row++) {
     for (int col = 1; col < 20; col++) {
         if(math[row][col]==1)demonstration++;}}
 QMessageBox *msg=new QMessageBox;
 msg->setText(QString::number(demonstration));
 msg->show();
 
}

#include<stdlib.h>
#include<qmessagebox.h>
#include<time.h>
void MainWindow::ButtonHandler()
        {
    int math[20][20];
    for (int row = 1; row < 20; row++) {
        for (int col = 1; col < 20; col++) {
            math[row][col]=0;}}
    int aux2=0;
    int aux3=0;
        srand(time(NULL));
        for(int i=0;i<100;i++)
{
bool set = false;
while(!set)
{
aux2=int( rand()%20);
aux3=int( rand()%20);
if(math[aux2][aux3]==0)
{
math[aux2][aux3] = 1;
set = true;
}
}

}
 int demonstration=0;
 for (int row = 1; row < 20; row++) {
     for (int col = 1; col < 20; col++) {
         if(math[row][col]==1)demonstration++;}}
 QMessageBox *msg=new QMessageBox;
 msg->setText(QString::number(demonstration));
 msg->show();

}

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and it dosn't all time give 100!!!(i'v made this program just to show you...)

[Archimedes]

1) Arrays in C/C++ always start from '0' not '1'
So in your loops is: for ( int row = 0; row < 20; ++row) { ... }

2) In lines 16-25 of the posted code, the moment you find a value of 0 and make it 1 you have also set=true which will terminate the loop. That is the loop will run only 1 time cause everything in the array is set to 0 and so the 1st value it'll find will be 0!!! So instead of checking the value set, make a variable that counts to 40 and then terminate the loop.

3) You **probably** not have exactly 40 values set to 1 because there's a possibility that aux2 and aux3 take values that points to an element already set to 1. If you have 39 elements set to 1 there's a ~10% possibility to select an element set to 1.

[SneakyPeterson]

2) In lines 16-25 of the posted code, the moment you find a value of 0 and make it 1 you have also set=true which will terminate the loop. That is the loop will run only 1 time cause everything in the array is set to 0 and so the 1st value it'll find will be 0!!! So instead of checking the value set, make a variable that counts to 40 and then terminate the loop.

That loop will run until a value is set to 1. It is SUPPOSED to terminate after setting exactly one value that is a 0 to 1. The fact that it gets called 100 times should guarantee that 100 seperate 0's are changed to 1. I think that the main reason that Hardstyle isn't always getting 100 1's is because he's ignoring a whole bunch of values by starting his arrays at 1 instead of 0. Of course you aren't going to find all 100 1's if you only check part of the array!

General structure of a for loop that iterates through an array should be:

for(int i = 0; i < count; i++)

NOT

for(int i = 1; i < count; i++)

[Hardstyle]

1) Arrays in C/C++ always start from '0' not '1'
So in your loops is: for ( int row = 0; row < 20; ++row) { ... }

2) In lines 16-25 of the posted code, the moment you find a value of 0 and make it 1 you have also set=true which will terminate the loop. That is the loop will run only 1 time cause everything in the array is set to 0 and so the 1st value it'll find will be 0!!! So instead of checking the value set, make a variable that counts to 40 and then terminate the loop.

3) You **probably** not have exactly 40 values set to 1 because there's a possibility that aux2 and aux3 take values that points to an element already set to 1. If you have 39 elements set to 1 there's a ~10% possibility to select an element set to 1.

2) In lines 16-25 of the posted code, the moment you find a value of 0 and make it 1 you have also set=true which will terminate the loop. That is the loop will run only 1 time cause everything in the array is set to 0 and so the 1st value it'll find will be 0!!! So instead of checking the value set, make a variable that counts to 40 and then terminate the loop.

That loop will run until a value is set to 1. It is SUPPOSED to terminate after setting exactly one value that is a 0 to 1. The fact that it gets called 100 times should guarantee that 100 seperate 0's are changed to 1. I think that the main reason that Hardstyle isn't always getting 100 1's is because he's ignoring a whole bunch of values by starting his arrays at 1 instead of 0. Of course you aren't going to find all 100 1's if you only check part of the array!

General structure of a for loop that iterates through an array should be:

for(int i = 0; i < count; i++)

NOT

for(int i = 1; i < count; i++)

dude i know that in c++ array like all programing languages starts with 0

and SneakyPeterson's is right about the "2)"
the "3)" is why i use that loop ...if the aux2 and aux3 gets a value that is allrdy 1 it will redo the random thing until it will find a value that is 0....


can u please stop answering newbish and give answers only if you have any idea about the problem?

[SneakyPeterson]

dude i know that in c++ array like all programing languages starts with 0

So then why are you starting your arrays at 1?

and SneakyPeterson's is right about the "2)"
the "3)" is why i use that loop ...if the aux2 and aux3 gets a value that is allrdy 1 it will redo the random thing until it will find a value that is 0....
can u please stop answering newbish and give answers only if you have any idea about the problem?

While Archimedes was incorrect about the function of the loop, he did correctly diagnose your original problem of starting your array at the wrong point and thus, missing several int's when counting the number of set 1's. Please note that because you start at 1 in your first array as well, you never completely initialize your array properly. Your last comments seem a bit hostile to people who are trying to help you solve your problem and in my opinion, have done so at this point.