CODEWITHSUNDEEP
c#while-loop
Code_Steel
Code_Steel

Reputation: 435

What's happening in this while-loop?

double number;
bool isParsed = false;

while(!isParsed)
{
    Console.WriteLine("Enter the value");
    isParsed = double.TryParse(Console.ReadLine(), out number);
    if(isParsed)
    {
        break;
    }
    Console.WriteLine("Invalid value");
}

A friend and I were studying this code block. I found this part to understand:

bool isParsed = false;

while(!isParsed)

I thought that if isParsed = false, and the while loop will check the negation (!isParsed) to see if it should run, wouldn't this be the logic:

while(!isParsed) => while(NOT(false)) => while (true)?

Therefore, the while loop would never run. But it does run. Later I understood that a check was happening:

while (!isParsed) => while((!isParsed) == true),

but he says that not exactly what is happening.

Can someone explain what is happening here?

Upvotes: 1

Views: 69

Answers (3)

ravinikam
ravinikam

Reputation: 3696

 bool isParsed = false;

while(!isParsed)

Loop should run, at least once; Which is correct behavior, since your condition is evaluating to true.

Upvotes: 1

Angelo DeMichaels
Angelo DeMichaels

Reputation: 251

When using a boolean in an expression you are checking for a value of true. When adding the logical NOT operator, you are now looking for a value of false.

while (false)

Upvotes: 2

Thomas Stringer
Thomas Stringer

Reputation: 5862

You're saying it correctly: while (true). That true boolean condition denotes that the next (and first) iteration will run.

!false == true

Take a look at the MSDN documentation stating the behavior of the while loop: https://msdn.microsoft.com/en-us/library/2aeyhxcd.aspx

Upvotes: 4

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