Creating a Vector variable | Together C & C++ | Page 1

south zealot Oct 30, 2023, 6:58 PM

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The question is listed below

whole shellBOT Oct 30, 2023, 6:58 PM

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south zealot Oct 30, 2023, 6:58 PM

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my attempt so far:

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typedef struct {
    int length;
    int *element;
} Vector;

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Vector createVector(const unsigned int nLength)
{
    float *array = malloc(nLength * sizeof(float));
}

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I'm lost in the second part where I have to create a vector variable using a function

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Can anyone give me a hint or sth? thanks

timber patrol Oct 30, 2023, 7:01 PM

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you need to allocate the pointer inside the Vector structure

south zealot Oct 30, 2023, 7:02 PM

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huh

timber patrol Oct 30, 2023, 7:02 PM

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Initially you have an empty istance of a Vector, then you malloc the "element" inside of it when you call createVector and assign length to the nLength parameter

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Then when you do destroyVector you must do a free of that Vector istance

south zealot Oct 30, 2023, 7:03 PM

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I'm sorry I don't quite catch that

timber patrol Oct 30, 2023, 7:03 PM

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I'll give you a piece of code

south zealot Oct 30, 2023, 7:03 PM

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sure

timber patrol Oct 30, 2023, 7:03 PM

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Without the solution because you need to understand

south zealot Oct 30, 2023, 7:03 PM

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ofc

timber patrol Oct 30, 2023, 7:07 PM

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{
    int size = 0; //empty
    int* elements = NULL; //empty
} Vector;


void createVector(Vector* input, int size)
{
    //malloc the input and insert the size

    //you not need to return anything because you have the reference of the outside vector
}

int main()
{
    Vector myVector;
    createVector(&myVector, 10); //create my vector of 10 elements
}```

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try to understand this

south zealot Oct 30, 2023, 7:07 PM

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sure thanks a lot

timber patrol Oct 30, 2023, 7:08 PM

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you have your instance in the main, you call the createVector that fulls the vector instance

south zealot Oct 30, 2023, 7:08 PM

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but in my hw it states that the input is only

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unlike your function where u can have an input and size

timber patrol Oct 30, 2023, 7:08 PM

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i'll rewrite for this case

south zealot Oct 30, 2023, 7:09 PM

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sure

timber patrol Oct 30, 2023, 7:09 PM

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{
    int size = 0; //empty
    int* elements = NULL; //empty
} Vector;


Vector createVector(const unsigned int nLength)
{
    Vector myVector;

    //malloc the elements inside the vector and insert the size

    return myVector;
}

int main()
{
    Vector myVector = createVector(10); //create my vector of 10 elements
}```

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there you go

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then after this try to delete it by yourself

south zealot Oct 30, 2023, 7:11 PM

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Oh now i get it, thanks.

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ill give it a go

timber patrol Oct 30, 2023, 7:11 PM

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try, compile it and run it

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a good thing is to do debugging to the code

south zealot Oct 30, 2023, 7:11 PM

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sure

timber patrol Oct 30, 2023, 7:11 PM

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in visual studio code

south zealot Oct 30, 2023, 7:12 PM

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cool

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Hey for freeing the vector,
can I just free the whole variable like this?

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void destroyVector(Vector vec)
{
    free(*vec);
}

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or should I free each of the members first then free the vec

timber patrol Oct 30, 2023, 7:15 PM

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you need to free the elements inside

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because the Vector itself is in stack

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elements is in the heap because you malloc it

south zealot Oct 30, 2023, 7:16 PM

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oh

timber patrol Oct 30, 2023, 7:16 PM

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when you malloc something you need to free, if you don't malloc you don't need to free

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that's the rule

south zealot Oct 30, 2023, 7:16 PM

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alright thanks

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!solved

whole shellBOT Oct 30, 2023, 7:17 PM

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#Creating a Vector variable