error : variable-sized object 'largeArray2' may not be initialized

Hi, when i compile my code i get this error : "error : variable-sized object 'largeArray2' may not be initialized"
I just don't understand this error, any help would be appreciated, thanks in advance.

Code:

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float give_coefficients_routh_table_and_fill_two_first_lines(int denominator_degree)
{
  float largeArray2[20][20] = {0};
  int l = 0;
  int c = 0;
  int e = denominator_degree ;
  for ( e = denominator_degree; e>=0; e--)
            {
            float array_of_coefficients[20];
            float d(e);
            cout << "what is the coefficient linked with degree" << e << "?" << endl;
            cin >> d;
            d = array_of_coefficients[e];
            if ( l==2 ){ l = 0; c++;}


                float largeArray2[l][c] = {d};
                l++;
            }
return largeArray2[20][20];
}

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Quote:

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Originally Posted by funnydarkvador

Code:

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float largeArray2[20][20] = {0};

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you're obviously declaring and initializing your array here. on which line does that warning message acctually occur?

Quote:

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Originally Posted by funnydarkvador

Code:

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cin >> d;
d = array_of_coefficients[e];

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I don't know what you're trying to achieve here. you're accepting input into d, and then overwriting that input with the value already stored in array_of_coefficients[e], which is uninitialized.

Quote:

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Originally Posted by funnydarkvador

Code:

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float largeArray2[l][c] = {d};

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what you're doing here is declaring a new array called largeArray2, with dimensions l and c. this is a new array, and the compiler doesn't care because it's in a new scope, distinct from where the previous largeArray2 array was declared.

Quote:

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Originally Posted by funnydarkvador

Code:

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return largeArray2[20][20];

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this is wrong. this will return a single float value, when I suspect you actually want to return the whole array. unfortunately, the compiler knows that you only declared the array as a float[20][20], and you're trying to return the last element of a float[21][21].

The only error is at this line :

Code:

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floatlargeArray2[l][c] = {d};

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I just want to give a value d (which is different each time in the loop because it is typed in by the user) to each cell of the array largeArray2 but i think the error is due to the fact that variables l and c are incremented, that's why i get the error error : variable-sized object 'largeArray2' may not be initialized

Please tell me how to do

The thing is, that line looks like an attempt to declare and initialise a variable length array named largeArray2, which hides the other array of arrays named largeArray2.

What you probably want to do is to assign the value of d to each element of largeArray2[l]. (By the way, l is a very bad variable name because on some fonts it looks like 1 (one). Your variable names should be descriptive.)

One way out is to use a simple loop to assign the values. Another option is to #include <algorithm> and use std::fill or std::fill_n. Of course, you would still have the last problem that Elkvis mentioned: your array is local.

Quote:

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Originally Posted by laserlight

The thing is, that line looks like an attempt to declare and initialise a variable length array named largeArray2, which hides the other array of arrays named largeArray2.

What you probably want to do is to assign the value of d to each element of largeArray2[l].

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Yes that's what i want to do, but i don't understand your idea to use a simple loop to assign the values, can you explain me a little bit please?

Quote:

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Originally Posted by funnydarkvador

Yes that's what i want to do, but i don't understand your idea to use a simple loop to assign the values, can you explain me a little bit please?

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Consider this program:

Code:

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#include <iostream>

int main()
{
    int numbers[10] = {0};

    // Only insert code below this point:
    // Only insert code above this point.

    for (int i = 0; i < 10; ++i)
    {
        std::cout << numbers[i] << ' ';
    }
    std::cout << std::endl;
}

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Insert code in the position indicated such that the program will print:

Code:

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0 1 2 3 4 5 6 7 8 9

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The code inserted must not print anything by itself.

[QUOTE=laserlight;1151378]Consider this program:

Code:

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    for (int i = 0; i < 10; ++i)
    {
        std::cout << numbers[i] << ' ';
    }
    std::cout << std::endl;
}

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I just don't understand the use of this part of the code : why do i need to display the cells of an array on 1 line :

1	0 1 2 3 4 5 6 7 8 9 i don't say your idea is stupid, it may be right actually, but i don't understand how to use it

[QUOTE=funnydarkvador;1151391]

Quote:

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Originally Posted by laserlight

why do i need to display the cells of an array on 1 line

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For the purpose of learning. Laserlight gave you an exercise that will help you learn. She is smart enough to avoid giving you a canned solution that you would simply copy, as you would learn nothing.


Incidentally, variable length arrays are a feature of C (after the 1999 C standard). They are not a feature of C++. What is why the compiler is complaining about your code.

Thank you for your advice laserlight. I think i don't need to use std::cout because i did #include <cstdlib> at the beginning of my program, so that i use cout whether than std::cout
Anyway i've discovered some errors in my program, and i'll show you the final version that works

Quote:

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Originally Posted by funnydarkvador

I think i don't need to use std::cout because i did #include <cstdlib> at the beginning of my program, so that i use cout whether than std::cout

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That is not correct. std is a namespace; including headers do not change what namespace anything lies in. cout lies in std, always will and always have.
Therefore, regardless of what headers you include, you must say std::cout.
Alternatively, you may use

using std::cout;
or
using namespace std;

And then you can type cout with "std::". The first approach is okay, but the second is not really recommended. It can cause a lot of name collisions. You should brush up your knowledge on namespaces and includes (headers).