Is there a difference in while() & do...while() loops?

Question

0.00/5 (No votes)

See more:

Okay silly question I have done the Software design courses where the mantra is do..while executes at least once, while() may never execute.
I have written an App thats has just started working for some reason after a morning of not working it has sprung into life(!) it started to work yesterday after fiddling with a while loop that had three bools in that were 'or'ed

C#

 if (Tolerance3 == false)
{
    DUT3 = Convert.ToInt16(txtDUTVal3.Text);
    Gold3 = Convert.ToInt16(txtGold3.Text);
    if (DUT3 < Gold3)
    {
        IncreaseDUT3();
    }
    if (DUT3 > Gold3)
    {
        DecreaseDUT3();
    }                  
    if ((!(DUT3 < GoldTol3Min)&&!(DUT3>GoldTol3Max)))
    {
        Tolerance3 = true;
        MessageBox.Show("Tolerance 3");
    }
    if (Tolerance3 == true)
    {
        MessageBox.Show("Tolerance3 = true");
        FileName = INIPath + "\\MagZero.txt";
        if (!File.Exists(FileName))
        {
            StreamWriter sw = new StreamWriter(FileName);
            sw.WriteLine("Mag Zero " 
                         + dt.ToString("M_d_yyyy_HH:mm") 
                         + "\n\t Sensor3: " 
                         + txtDUTVal3.Text 
                         + " PWM Value: " 
                         + txtPWMvalue3.Text 
                         + "\n");
            sw.Close();
        }
        else
        {
            StreamWriter sw = File.AppendText(FileName);
            sw.WriteLine("\n" 
                         + "\n\t Sensor3: " 
                         + txtDUTVal3.Text 
                         + " PWM Value: " 
                         + txtPWMvalue3.Text 
                         + "\n");
            sw.Close();
        }
    }
}

wasn't executing now it has started. WHY?, WHY? I can't ship code that won't reliably work. The value can be seen to change but not always evaluated while the first two versions of this work like a charm I am wondering if C# gets an interrupt jumps to the service routine and then returns sees one of the coditions of the while met a leaves it, or gets another interrupt and ignors the rest of the while loop conditions

Glenn

Posted 30-Sep-10 1:21am

glennPattonWork3

Updated 30-Sep-10 1:39am

#realJSOP

v2

Add a Solution

Comments

ARopo 30-Sep-10 7:31am

Have you posted the correct code? I can't see any while loops here

3 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

#realJSOP · Answer 1 · 2010-09-30T01:36:00

A while() loop will not run unless the codition is true. A do...while() loop will always run at least once.

The following will run at least one time

bool x = true;
while (x)
{
    // do something that could possibly change x to false
}

The following while loop will not execute because the condition is false.

bool x = false;
while (x)
{
    // do something that could possibly change x to false
}

The following will always execute at least once

bool x = true;
do
{
    // do something that may change the value of x
} while (x);

That's the primary difference between the two.

You can also use break or continue inside those loops to short-circuit code to either exit the loop or start a new iteration.

Lastly, you can do this:

while (true)
{
}

...or this:

do
{
} while (true);

It creates a loop that keeps going until it encounters a break statment.

shakil0304003 · Answer 2 · 2010-09-30T01:49:00

Solution 4

Example :

int x = 6;

while (x <= 5)
{
Console.WriteLine("while "+x);
x++;
}

x = 6;

do{

Console.WriteLine("Do While "+x);
x++;
}while(x<=5);

see the output of this code, then you will understand the difference.

Posted 30-Sep-10 1:49am

shakil0304003

Comments

glennPattonWork3 30-Sep-10 8:09am

Yeah, I know that what I'm wondering is if you have multiple conditions in your while not just one are they evaluated seperatly.

Glenn

#realJSOP · Answer 3 · 2010-09-30T01:46:00

Solution 3

First, change this:

if ((!(DUT3 < GoldTol3Min)&&!(DUT3>GoldTol3Max)))    
{
    Tolerance3 = true;
    MessageBox.Show("Tolerance 3");
}

to this:

if (DUT3 >= GoldTol3Min && DUT3 <= GoldTol3Max)
{
    Tolerance3 = true;
    MessageBox.Show("Tolerance 3");    
}

Second, there's no wy we can tell you why your code just starts to work on its own. We don't knwo ANYTHING about the rest of the code.

Posted 30-Sep-10 1:46am

#realJSOP

Comments

glennPattonWork3 30-Sep-10 7:55am

if C# gets an interrupt jumps to the service routine and then returns sees one of the coditions of the while met a leaves it, or gets another interrupt and ignors the rest of the while loop conditions, that is really what I'm wondering if the while() is evaluated seperatly! a=b & a=c is it (a=b), true/false and the (a=c) can it be interrupted or is it treated as a whole?

glennPattonWork3 30-Sep-10 9:06am

Well I have tried the above method >= & <= with no luck, since that change DUT3 has started not behaving as well.

#realJSOP 1-Oct-10 14:16pm

Then you have bigger problems. BTW, I woudl use Int32.TryParse() if you're converting from a string to an int. That way, you could head-off problemns with invalid characters in the string.

Is there a difference in while() & do...while() loops?

3 solutions

Solution 1

Solution 4

Solution 3

Add your solution here

Preview 0

Existing Members

...or Join us