Discovered code

15y845Azure

Hi Vulpes,

I saw the following code you published on an answer and just wonder if you could explain it please bit by bit, I have put my answers below each line of code as to what I think...

Array temp = (Array)mySectionList.D;

// Creating a variable named temp of type Array which is cast to Array. Thinking mySectionList.D is a class with a static method?

double[] myDs = new double[temp.GetLength(0)];

// A new instance of type double with myDs as variable, temp is a field or property with GetLength which is derived from system.object?

for(int i = 1; i <= temp.GetLength(0); i++)
{
myDs[i - 1] = (float)temp.GetValue[i];
}

// a loop of which the integer 1 is less or equal to the GetLength arguement 0?

Regards,

9 Replies

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Vulpes15y ago
Accepted answer
You've chosen some fairly unusual code here.

In the first line:

Array temp = (Array)mySectionList.D;

mySectionList.D is in fact an instance property of type 'dynamic' which actually holds a 1-based array of floats. As this is something which C# syntax can't cope with we were trying to cast it to the generic Array type and then assign it to the Array variable 'temp'. This didn't work (don't worry it's strange COM stuff!) and it was necessary to cast it to object first and then to Array.

In the second line:

double[] myDs = new double[temp.GetLength(0)];

we're creating a new double array with the same length as the 'temp' array and assigning it to the variable myDs.

In the loop:

for(int i = 1; i <= temp.GetLength(0); i++)
{
myDs[i - 1] = (float)temp.GetValue[i];
}

the loop variable 'i' is ranging from 1 to the length of the 'temp' array, and then myDs's (i -1)th element is being populated with the element at index 'i' in the temp array. As we're using GetValue() - which returns an object - rather than normal array syntax, it's necessary to cast to float first.
Vulpes15y ago
What that piece of code was trying to do was to fill a zero-based float array (namely myDS) with the corresponding values from a 1-based float array (namely temp). So the for loop was ranging from 1 to temp.GetLength(0) and, since we were using i - 1 for the index of myDS, the latter was ranging from 0 to temp.GetLength(0) - 1.

We could have done it the other way around - there are nearly always several ways to do the same things in programming :)
15y ago
So in theory could the code be written as

if (i == temp.getLength(0));

return i;

I dont understand why 1 would need to be looped, is it because mySectionList.D holds a 1-based array of floats which is what is being looped?

Regards,
Vulpes15y ago
Well, the condition i <= temp.GetLength(0) is checked each time through the loop including the first time.

Also i is increased by one each time through the loop except the first time.

By the time i has reached temp.GetLength(0) + 1, the condition fails and the loop stops.
15y ago
when would the loop know when it gets to test.GetLength(0); as 1 is obviously an integer?
Vulpes15y ago
It's 'i' that's the control variable of the 'for' loop.

It starts off at 1 and is then incremented by 1 each time around the loop until it reaches temp.GetLength(0) and the loop terminates.
15y ago
Vulpes

In regards to the for loop, is it i or 1 that loops through the temp array?

Regards,
Vulpes15y ago
Yeah, it's unusual code in that we don't normally have to deal in C# with arrays which have a lower bound of 1 rather than 0. However, this sort of stuff is commonplace in COM and so, when doing COM interop, we need to find a way around it :)
15y ago
Hi Vulpes,

Many thanks for your answers there its really starting to fall into place for me now.

Unusual code in the sense that is not commonly practiced? - sorry for this, its just im trying to learn C# in depth! : )