Question like in title. What is exactly happening when Write method is invoked? If I have code like this:
int [] t = new int[]{2,1};
Console.Write(t);
is there any posibility that without changing Write method parameter (without adding [0]) number 2 will be displayed? (first element of array) Will this code give the same result in different .NET framework versions?
Why this method doesn't write type of y? (System.Int32[])
No that is not really possible since you would have to redefine the toString() method of Int32[].
Console.Write(t) is simply Console.Write(t.toString()) and t.toString() is Int32[].toString().
The behavior of Int32[].toString() is to simply return the type, in this case System.Int32[].
So to answer your question, no you cannot make the Int32[].toString() return the toString() of the first index.
Related
I have several times used the expression anArray.[i] to access an element from an array.
but all the sudden when i try to make a very very simple function then i get an error.
let safeIndexIf anArray i =
anArray.[i]
I need to make a function that returns the ith element of the array so i thought that was an easy one but no...
The Error:
The operator 'expr.[idx]' has been used on an object of indeterminate type based on information prior to this program point. Consider adding further type constraints
Why is this not working? I dont know what the error means by that. All i know i have done something similar to this lots of times to access an element of anArray so why can't i this time?
It means the compilers type inference cannot determine that anArray is indeed an array.
The error message is suggesting you add a type annotation, you could do something like this to say that anArray is a generic array:
let safeIndexIf (anArray : array<'a>) i =
anArray.[i]
If you want to avoid type annotations you could try rewriting your function to use Array.item which has the same behaviour:
let safeIndexIf anArray i =
Array.item i anArray
I have the following nested struct:
hole 1x200 struct, diam 1x12 struct, which has the following fields: pos, freq1, fre12
That is:
hole(1 to 200).diam(1 to 12).pos
.freq1
.freq2
From a value (freq1 and freq2), I would like to obtain the field name of the struct. So I will need to find the value that matches with freq1 and freq2 and show the fieldname.
I tried to use structfun in order to apply a function to each field.
[struct.field]=structfun(#(x) find(x.freq1==27.059783995484867 & freq2==76.468355874897000))
But I guess I am writing something wrong on the code.
Also I create an anonymous fuction but I have the following error:
'Error using structfun / Inputs to STRUCTFUN must be scalar
structures'
. How ever when I verified if an specific value of the struct is scalar, I have a positive answerd: isscalar(hole(130).diam(10))
I belive I more near the solution using this script:
myfun=#(yourarray,desiredvalue) yourarray==desiredvalue;
%//Apply function to each field of scalar structure, it SCALAR??
desiredfieldindex=myfun(structfun(#(x) x,hole),26.697046257785030)
desiredFieldName=fNames(desiredFieldIndex)
I don´t know if I am in the rigth path, or I should utilize the function find. ALso I that case I don´t know how to implement it.
Couple of things.
FLOATING POINT VALUES! Careful!! Never compare a floating point value as val==0.3! do abs(val-0.3)<10^-8 or something similar. Read more here.
You are using structfun wrong. The function needs 2 arguments, and you are just passing 1! However, structfun will apply a function to each field so you are not using it rigth either in that sense. Lets see an example
example:
a.hithere=5;
a.notthis=3;
fun=#(x)x==5;
[isfive]=structfun(fun,a)
isfive =
1
0
As you can see, it applies the function to each of them. If you try to change the function to fun=#(x)x.hithere==5 you will get an error! As the function is applied to each field, and x.hithere.hithere or x.notthis.hithere do not exist.
If you want to check both values, you will need to check them independently making two separated calls to structfun or avoiding structfun and just making a for loop.
i mean is it possible to have a method that gets as its parameters an array of objects and another parameter which indicates which field of the objects we are using to sort the array ?
for example if the objects are contacts if we call sort(contacts , name) it would sort them with respect to name. if we call sort(contacts , number) it sorts them according to their numbers.
maybe by sending an String of the field we want !! something like :
class sorting {
public static bubble_sort(Object[] array , String field){
for(int i =0; i<array.length ; i++){
if(array[i].field > array[i+1].field)
swap(array ,i ,i+1);
}
}
(preferably in java) (and please include examples of the solutions you give !)
Assuming this is Java: yes, it is possible. You can use reflection to get the field type and value and then compare them. It would not be a good idea. Much better to use Comparator with the existing sort method.
A method that would work in pretty much any language is to pass in some kind of function object.
class sorting {
public static bubble_sort(Object[] array, FunctionObject ordering) {
for(int i =0; i<array.length ; i++){
if(ordering(array[i+1], array[i]))
swap(array ,i ,i+1);
}
};
different languages are going to have different syntaxes for such a function object -- what its type is, etc -- but pretty much every language is going to have some way to do it.
Generally the best signature for it is one that takes two different objects, and returns true if the left one is less than the right one.
Similarly, different languages are going to have different ways of invoking a function object. Some may require ordering.Invoke( array[i+1], array[i] ).
In that function object, compare the field in question. If the language/objects have reflection, you can sometimes do this via field name directly.
As this pattern is very useful, languages tend to make it easier as they mature. So the most recent version of your language may have a syntax to create such objects with far less syntax, and invoke them with less syntax as well.
Apologies if I am making some amateur mistakes, but I am new to VBA.
I'm trying to populate an array declared inside of a class as a property, but something's going wrong. After much searching I have two questions that I can't seem to find anywhere else:
1 - Is there a simpler way to accomplish saving data to an array-like structure that I can pass to functions from a sub? The array-like structure needs to be resizable because I will not know how many components I will add until each iteration of a loop checks those conditions.
2 - How do I correctly accomplish the passing of the array property in my class correctly to another function? It's frustrated me enough that I would like to know how it can be done if only to understand what I was doing wrong or, perhaps, what misunderstanding I had of the way VBA works.
Code structure follows:
I have declared a Segments property inside of a CTask class like this:
Private pSegments() As CSegment
Public Property Get Segments() As CSegment()
Segments = pSegments()
End Property
Public Property Get segment(index As Integer) As CSegment
segment = pSegments(index)
End Property
Public Property Let Segments(Value() As CSegment)
pSegments() = Value()
End Property
I pass the CTask from a Sub, where it is defined to populateTasks using this code:
Dim tasks() As CTask
ReDim tasks(1 To 10)
Call populateTasks(tasks)
When I do this, the populateTasks code receives it using the following code:
Function populateTasks(ByRef tasks() As CTask)
I then try to call another function from populateTasks called populateSegments like this:
Call populateSegments(tasks(icount).Segments)
I receive segments array inside populateSegments like this:
Function populateSegments(ByRef Segments() As CSegment)
The last two code snippets are where the problem resides. The segments array is populating correctly inside the populateSegments function, but when I check the array to see if it is empty just below the call to populateSegments there isn't anything in the tasks(icount).segments array. Thanks in advance for any help, and please let me know if more information is required.
Couldn't you make populatesegments a method of cTask? That avoids the problem and is a better design
I started learning C in class and have started the assignment but I'm writing it one piece at a time. Currently I'm stuck because I may be doing something completely wrong but I don't know what I'm doing.
The error is pretty clear... The void type isn't something you can return / store in a variable. Instead it's a special type that means "nothing". You can't store nothing, you must ignore the return or return something.
displayCard only displays the cards, it does nothing to define them, so you shouldn't be trying to use it to create your cards. Instead, think about what a "card" actually is in your program--what, for example, do you have to pass to displayCard in order for it to know which card to display?