c# if statement inside while loop how to break out if user inputs valid data

Question

I would like to know what to put in the if statement brackets to tell the program, if x or y equals a double, it can break out and continue carrying out the rest of my code.

Any suggestions?

while (true)
{                    
    Console.Write("I need to pour this much from this one: ");

    string thisOne = Console.ReadLine();
    Double.TryParse(thisOne, out x);

    if ( /* Here I want to put "x is a number/double*/ )
    {
        break;
    }

}

while (true)
{
    Console.Write("I need to pour this much from that one: ");

    string thatOne = Console.ReadLine();
    Double.TryParse(thatOne, out y);

    if (/* Here I want to put "y is a number/double*/)
    {
        break;
    }
}

My suggestion is to read the documentation for Double.TryParse. Hint: It returns a boolean. — D Stanley
– D Stanley, Commented Jul 23, 2014 at 12:27

Sayse · Accepted Answer · 2014-07-23 12:26:26Z

4

TryParse returns a boolean to say whether the parse was successful

if (Double.TryParse(thatOne, out y))
{
    break;
}

From documentation

A return value indicates whether the conversion succeeded or failed.

answered Jul 23, 2014 at 12:26

Sayse

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Comments

James · Accepted Answer · 2014-07-23 12:26:38Z

2

Double.TryParse returns a boolean, perfect fit for your if statement

if (Double.TryParse(thatOne, out y)) {
    break;
}

answered Jul 23, 2014 at 12:26

James

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Comments

Marco · Accepted Answer · 2014-07-23 12:47:06Z

2

You have a misconception about TryParse(). You want to check if x is a double. somewhere above in your code, you did not post it here there is probably a line like double x = 0;. You defined x and y already as double. You want to check if your input which is string can be parsed to double:

The shorthand version is this:

if (Double.TryParse(thatOne, out x))
{
    break;
}

This can also be written as:

bool isThisOneDouble = Double.TryParse(thisOne, out x);

if (isThisOneDouble)
{
    break;
}

If you really want to check if a variable is of certain type without trying to parse it, try it like this:

double x = 3;
bool isXdouble = x.GetType() == typeof(double);

or

double x = 3;
if(x.GetType() == typeof(double)) 
{
   // do something
}

edited Jul 23, 2014 at 12:47

answered Jul 23, 2014 at 12:33

Marco

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Comments

artragis · Accepted Answer · 2014-07-23 12:28:07Z

0

According to the documentation, TryParse returns true if parsing succeeded so just put your tryparse into your if statement.

answered Jul 23, 2014 at 12:28

artragis

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Comments

D Stanley · Accepted Answer · 2014-07-23 12:44:03Z

0

Control your loop with a bool, set the bool false when your condition is met...

bool running = true;
while (running)
{                    
    Console.Write("I need to pour this much from this one: ");

    string thisOne = Console.ReadLine();

    if (Double.TryParse(thisOne, out y))
    {
         running = false
    }
}

edited Jul 23, 2014 at 12:44

D Stanley

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answered Jul 23, 2014 at 12:27

kidshaw

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3 Comments

James Over a year ago

Seems like an unnecessary step? This also requires the loop to perform a full iteration, the OP might want to break out early.

Sayse Over a year ago

It also doesn't answer the question of what goes into the if statement.

kidshaw Over a year ago

Just edited to include, missed that from the original question. The last step is a break so not adding extra execution.

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