Is it possible to loop a switch?

[marknyc]

I'm writing a program and I'm wondering if it's possible to loop a switch because my program is suppose to emulate a process going into the critical section of a computer. Something like this:

=========================================
You are in the critical section Reader 2
=========================================

=========================================
You are in the critical section Reader 2
You are in the critical section Reader 5
=========================================

=========================================

You are in the critical section Reader 2
You are in the critical section Reader 5
You are in the critical section Writer 2
=========================================


Until it is eventually full which would be with 3 readers and 3 writer


Thanks
If anyone can help it would be greatly appreciated

[Disch]

Sure you can loop a switch. Just put your switch in a loop.

Or am I misunderstanding?

[marknyc]

I tired that but it doesn't seem to restart and give me new information is simply prints this:

============================
You are in the critical section Reader 2
You are in the critical section Reader 2
You are in the critical section Reader 2
You are in the critical section Reader 2
You are in the critical section Reader 2
You are in the critical section Reader 2
You are in the critical section Reader 2
You are in the critical section Reader 2
You are in the critical section Reader 2
You are in the critical section Reader 2
You are in the critical section Reader 2
=============================

For how ever long the loop is set for

[Disch]

Well you're probably not recording the information right.

I won't be able to help without seeing a small section of code showing the basic idea of what you're trying to do.

[marknyc]

The code is posted below. I 'm using the rand() function to autocailly select a case in the swtcih to print out. but unfortunately it stays on one during it's loop.

Thanks



#include <iostream.h>
#include <fstream>
using namespace std;


int main()
{





int x, choice;
srand(time(NULL));
x = rand() % 8 + 1;
int count = 0;


ofstream outfile ("readers.txt",ios :: out);






switch (x)
{
while (true)
{
case 1: outfile << "You are in Reader's 1 Critical section" <<endl ; //return 0;
break;
case 2: outfile << "You are in Reader's 2 Critical section" <<endl;//return 0;
break;
case 3: outfile << "You are in Reader's 3 Critical section" <<endl; //return 0;
break;
case 4: outfile << "You are in Reader's 4 Critical section" << endl;//return 0;
break;
case 5: outfile << "You are in Reader's 5 Critical section" << endl;//return 0;
break;
case 6: outfile << "You are in Writer's 1 Critical section" <<endl ;//return 0;
break;
case 7: outfile << "You are in Writer's 2 Critical section" <<endl;//return 0;
break;
case 8: outfile << "You are in Writer's 3 Critical section" <<endl; //return 0;
break;
}
}




count++;

outfile << count << endl;
outfile<< x << endl ;

}

[Disch]

There are a few things wrong with this:

1) You put the loop in the switch. You're supposed to put the switch in the loop.

2) you're not looping your input, so x will never change, so you'll always print the same thing over and over.


Whatever you want to happen multiple times -- that is what needs to be inside the loop:

while(true)
{
  x = /*change x somehow */;
  switch(x)
  {
    //check the new value of x
  }
}

[marknyc]

I will give it a shot thanks

[marknyc]

Thank you it works

[marknyc]

Its there anyway to keep them as a group meaning the first time it goes around it gets


============================
You are in the critical section Reader 2 First run
============================


============================
You are in the critical section Reader 2 Second run
You are in the critical section Reader 5
===========================

===========================
You are in the critical section Reader 2 Third run
You are in the critical section Reader 5
You are in the critical section Writer 2
===========================

[Disch]

I don't really understand what you mean, sorry.

Do you mean you want to remember the output of the program from the last time it was run?

[marknyc]

Yes. I was looking into nested loops but it doesn't seem to work.

[Disch]

Looking back, I don't even understand what I was asking before. hahah oh well.

If you want the program to remember something, you need to put it in memory (ie: a variable).

If there's a fixed maximum that you're going to have to remember, the most basic way is to just use an array:

int output[20];  // no more than 20 numbers to be remembered
int count = 0;  // how many have been remembered

while(count < 20)
{
  int x = /*whatever*/;
  output[count] = x;
  ++count;
}

Or if you want to get into STL, a better way to go would probably be a deque or a vector. This lets it dynamically grow as you add number so there's no fixed maximum like there is with an array:

#include <deque>
using namespace std;

...

deque<int> output;

while( /*whatever*/ )
{
  int x = ...
  output.push_back(x);
}

You can then use an iterator to step through the deque and output all the numbers.

-------------------------

Now if you were talking about saving the program output so that when the program closes and is reopened it remembered what it output last time, you'll need to save the output to a file and then reload it in the program. But that's another topic I don't care to get into.

[marknyc]

Sorry it didn't work what i was basically looking for was something like this

*
**
***
****
*****
******
*******
********

every time the loop runs the * is incremented and saved. i wanted keep it all in a group.

[marknyc]

Or more like this:

11
11 12
11 12 13
11 12 13 14
11 12 13 14

[Disch]

Right. That's what I was showing.

Of course recording it is only half. When you output you'd have to traverse the array and output each element.

[marknyc]

I saw just wondering why this doesn't work

for( m=1; m<100; m++)

{
for(n=1; n<100; n++)
{


maybe because it's a switch?

[Disch]

Switch has nothing to do with it.

Nested loops do work. And you probably want to do something like that. But you have to arrange everything properly. Your code is probably all misplaced.

I get the impression you're trying random things and going "well that didn't work", and then just trying something else. This hardly ever leads to a solution.

In order to program you need to understand that the computer is very stupid. You have to tell it every little thing you want it to do. It doesn't know how to do anything on its own.

The upside to this is that if you understand the code you're writing you can see what the computer will do before you actually run the program. This is why you need to really understand how loops (and all control structures) work.


If the program doesn't do what you expect, instead of trying random changes, try stepping through the code on your own. Pretend you are the computer and you have to run this program.

Let's try this. Let me see your new code and I'll walk through it with you and point out exactly what the computer is doing. That way you can see why things aren't working the way you expect them to.

[marknyc]

#include <iostream>
#include <fstream>
using namespace std;


int main()
{





int x, n =1 , m =1;




ofstream outfile ("readers.txt",ios :: out);

srand(time(NULL));
int count = 0 ;





for( m=1; m<100; m++)

{
for(n=1; n<100; n++)

{
count++;
outfile << "=====================================================" <<endl;
outfile << count << endl;
x = rand() % 8 + 1;

switch (x)
{



case 1: outfile << "You are in Reader's 1 Critical section" <<endl ;
break;
case 2: outfile << "You are in Reader's 2 Critical section" <<endl;
break;
case 3: outfile << "You are in Reader's 3 Critical section" <<endl;
break;
case 4: outfile << "You are in Reader's 4 Critical section" << endl;
break;
case 5: outfile << "You are in Reader's 5 Critical section" << endl;
break;
case 6: outfile << "You are in Writer's 1 Critical section" <<endl ;
break;
case 7: outfile << "You are in Writer's 2 Critical section" <<endl;
break;
case 8: outfile << "You are in Writer's 3 Critical section" <<endl;
break;

outfile << "=====================================================" <<endl;
}
}


}
}

[chrisname]

That's better; although I still don't understand what this "critical section stuff is."

[marknyc]

well I'm trying to get the for statement to work where it keep the statement from the from loop and brings in into the second loop and so on but it doesn't work i still get the same output.