Use [**`fabs()`**](http://en.cppreference.com/w/c/numeric/math/fabs) (in &lt;kbd&gt;math.h&lt;/kbd&gt;) to get absolute-value for `double`:

    double d1 = fabs(-3.8951);

Use `fabs` instead of `abs` to find absolute value of `double` (or `float`) data types. Include the `&lt;math.h&gt;` header for `fabs` function.  

    double d1 = fabs(-3.8951);

It&#39;s worth noting that Java can overload a method such as `abs` so that it works with an integer or a double. In C, overloading doesn&#39;t exist, so you need different functions for integer versus double.

I have found that using `cabs(double)`, `cabsf(float)`, `cabsl(long double)`, `__cabsf(float)`, `__cabs(double)`, `__cabsf(long double)` is the solution

      
      //use fabs()
      double sum_primary_diagonal=0;
      double sum_secondary_diagonal=0;
      double difference = fabs(sum_primary_diagonal - sum_secondary_diagonal);

I am looking for a PyQt5 tutorial. It is rather complicated to start GUI development with Python for the first time without a tutorial.

I only found some PyQt4 tutorials so far, and since something changed from Qt4 to Qt5, for example the fact `SIGNAL` and `SLOT` are no more supported in Qt5, it would be nice to have specific tutorials for PyQt5.

Can someone please provide a tutorial on how to start GUI development with PyQt5?

Is there a tutorial specifically for PyQt5?

How to do code something like this in `groovy`?

    do {
    
      x.doIt()
    
    } while (!x.isFinished())

Because there is *no `do ... while` syntax* in groovy.

&gt; **No &#39;do ... while()&#39; syntax as yet.**
&gt;
&gt; Due to ambiguity, we&#39;ve not yet added support for do .. while to Groovy

References:

 * [groovy - dev](http://groovy.329449.n5.nabble.com/) &gt; [do while](http://groovy.329449.n5.nabble.com/do-while-td4981923.html)
 * [Migration From Classic to JSR syntax](http://groovy.codehaus.org/Migration+From+Classic+to+JSR+syntax?print=1)
 * [Groovy Documentation](http://groovy-lang.org/documentation.html) &gt; [Control Structures](http://groovy-lang.org/semantics.html#_control_structures) &gt;  [Looping](http://groovy-lang.org/semantics.html#_looping_structures)
 * [Rosetta Code](http://rosettacode.org/wiki/Rosetta_Code) &gt; [Loops/Do-while Groovy](http://rosettacode.org/wiki/Loops/Do-while#Groovy)

Elegant way for do ... while in groovy

I want the absolute-value from a negative double - and I thought the `abs`-function was as easy to use as in java - but NOT!

It seems that the `abs`-function returns an int because I have the value 3.8951 and the output is 3.000000

    double d1 = abs(-3.8951);
    printf(&quot;d1: ...%lf&quot;, d1);

How can I fix this problem? That is - I want the absolute value of a `double`.

How to get absolute value from double - c-language

I want the absolute-value from a negative double - and I thought the <code>abs</code>-function was as easy to use as in java - but NOT!
It seems that the <code>abs</code>-function returns an int because I have the value 3.8951 and the output is 3.000000
<pre><code class="hljs language-scss">double d1 = abs(-3.8951);
printf("d1: ...%lf", d1);
</code></pre>
How can I fix this problem? That is - I want the absolute value of a <code>double</code>.

How can I print the result of sizeof() at compile time in C?

For now I am using a static assert (home brewed based on other web resources) to compare the sizeof() result to various constants.  While this works...  it is far from elegant or fast.  I can also create an instance of the variable/struct and look in the map file but this is also less elegant and fast than a direct call/command/operator.  Further, this is an embedded project using multiple cross-compilers...  so building and loading a sample program to the target and then reading out a value is even more of a hassle than either of the above.

In my case (old GCC), `#warning sizeof(MyStruct)` does not actually interpret sizeof() before printing the warning.

How can I print the result of sizeof() at compile time in C?

For a `char []`, I can easily get its length by:

	char a[] = &quot;aaaaa&quot;;
	int length = sizeof(a)/sizeof(char); // length=6

However, I cannot do like this to get the length of a `char *` by:

	char *a = new char[10];
	int length = sizeof(a)/sizeof(char);

because, I know, `a` here is a pointer, such that `length` here will be always be `4` (or something other in different systems).

My question is that how can I get the length of a `char *` afterwards? *I know someone may challenge me that you already know its `10` because you just created it. I want to know this because this step of getting its length may come long long way from its creation and I don&#39;t want to come long long way back to check this number. Moreover, I also want to know its real length.*

To be more specific

* how can I get its real `length=5`?
* how can I get its total `length=10`?

for the following example:

	char *a = new char[10];	
	strcpy(a, &quot;hello&quot;);



How to get the real and total length of char * (char array)?

I was surprised by this code:

    if (a =! b) { // let it be on false
        ...
    }

But `a` is never assigned by a value. What&#39;s this operator about?

What&#39;s this =! operator?

In a Linux C program, how do I print the thread id of a thread created by the pthread library? For example like how we can get pid of a process by `getpid()`.

How to get thread id of a pthread in linux c program?

The [bind()][1] function accepts a pointer to a `sockaddr`, but in all examples I&#39;ve seen, a `sockaddr_in` structure is used instead, and is cast to `sockaddr`:

    struct sockaddr_in name;
    ...
    if (bind (sock, (struct sockaddr *) &amp;name, sizeof (name)) &lt; 0)
    ...

I can&#39;t wrap my head around why is a `sockaddr_in` struct used. Why not just prepare and pass a `sockaddr`?

Is it just convention?

  [1]: http://linux.die.net/man/2/bind

Why do we cast sockaddr_in to sockaddr when calling bind()?

My question is that

I have a size_t data, but now I want to convert it to double or int.

If I do something like 

     size_t data = 99999999;
     int convertdata = data;

the compiler will report warning. because it maybe overflow.

Do you have some method like the boost or some other method to do the convert?


How to cast the size_t to double or int C++

I&#39;m learning swift recently, but I have a basic problem that can&#39;t find an answer

I want to get something like 

    var a:Int = 3
    var b:Int = 3 
    println( pow(a,b) ) // 27

but the pow function can work with double number only, it doesn&#39;t work with integer, and I can&#39;t even cast the int to double by something like Double(a) or a.double()...

Why it doesn&#39;t supply the power of integer? it will definitely return an integer without ambiguity !
and Why I can&#39;t cast a integer to a double? it just change 3 to 3.0 (or 3.00000... whatever)

if I got two integer and I want to do the power operation, how can I do it smoothly?

Thanks!


 

How to get the Power of some Integer in Swift language?

Recently I have had to serialize a double into text, and then get it back. The value seems to not be equivalent:

    double d1 = 0.84551240822557006;
    string s = d1.ToString(&quot;R&quot;);
    double d2 = double.Parse(s);
    bool s1 = d1 == d2;
    // -&gt; s1 is False

But according to [MSDN: Standard Numeric Format Strings][1], the &quot;R&quot; option is supposed to guarantee round-trip safety.

&gt; The round-trip (&quot;R&quot;) format specifier is used to ensure that a numeric value that is converted to a string will be parsed back into the same numeric value

Why did this happen?

  [1]: https://msdn.microsoft.com/en-us/library/dwhawy9k(v=vs.110).aspx#Anchor_8

Why is a round-trip conversion via a string not safe for a double?

Before I updated xCode 6, I had no problems casting a double to a string but now it gives me an error

    var a: Double = 1.5
    var b: String = String(a)

It gives me the error message &quot;double is not convertible to string&quot;. Is there any other way to do it?

Swift double to string

I know the `0.1` decimal number cannot be represented exactly with a finite binary number ([explanation][1]), so `double n = 0.1` will lose some precision and will not be exactly `0.1`. On the other hand `0.5` can be represented exactly because it is `0.5 = 1/2 = 0.1b`.

Having said that it is understandable that adding `0.1` **three times** will not give exactly `0.3` so the following code prints `false`:

    double sum = 0, d = 0.1;
    for (int i = 0; i &lt; 3; i++)
        sum += d;
    System.out.println(sum == 0.3); // Prints false, OK

But then how is it that adding `0.1` **five times** will give exactly `0.5`? The following code prints `true`:

    double sum = 0, d = 0.1;
    for (int i = 0; i &lt; 5; i++)
        sum += d;
    System.out.println(sum == 0.5); // Prints true, WHY?

If `0.1` cannot be represented exactly, how is it that adding it 5 times gives exactly `0.5` which can be represented precisely?


  [1]: http://www.exploringbinary.com/why-0-point-1-does-not-exist-in-floating-point/

Content Type	Original Author	Original Content on Stackoverflow
Question	user3155478	View Question on Stackoverflow
Solution 1 - C	herohuyongtao	View Answer on Stackoverflow
Solution 2 - C	haccks	View Answer on Stackoverflow
Solution 3 - C	lurker	View Answer on Stackoverflow
Solution 4 - C	Firas Nomaan	View Answer on Stackoverflow
Solution 5 - C	Md.Rakibuz Sultan	View Answer on Stackoverflow

How to get absolute value from double - c-language

C Problem Overview

C Solutions

Solution 1 - C

Solution 2 - C

Solution 3 - C

Solution 4 - C

Solution 5 - C

Elegant way for do ... while in groovy

Is there a tutorial specifically for PyQt5?

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