C++ declaring array while the program is running

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How can i declare an array while the program is running?
Something like :

C++

std::cin>> l ;
int array[l] ;

It doesn't work, it gets an Intelisence Err,

Expression must have an instance value.

I'm using visual studio 2010.

Thank you,

Posted 25-Apr-13 5:41am

m.r.m.40

Updated 25-Apr-13 5:47am

v2

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2 solutions

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Ian A Davidson · Accepted Answer · 2013-04-25T06:04:00

Solution 2

An alternative to using new and delete is to use the STL (standard template library) vector class - then you don't need to worry about deallocating since the vector class handles it.
E.g.

C++

#include <vector>

void foo()
{
    std::cin >> len;
    std::vector<int> a(len);
    // use the array "a"...
}

Regards,
Ian.

Posted 25-Apr-13 6:04am

Ian A Davidson

Updated 25-Apr-13 11:01am

v3

Comments

H.Brydon 25-Apr-13 12:14pm

Right on both counts. Thanks for the update on my answer.

Ian A Davidson 25-Apr-13 17:01pm

Any time.
Ian.

nv3 25-Apr-13 12:21pm

Good idea to use std::vector, although most beginners are overwhelmed with STL's complexity. Just as a comment: "array" is no C++ keyword, just a data type used in C++/CLI. But I agree, it would not be a good idea to give that name to a program variable.

Ian A Davidson 25-Apr-13 16:59pm

Good point. I was wondering about it - I just noticed that the encoding on this page turned it blue and looked it up here: http://msdn.microsoft.com/en-GB/library/2e6a4at9(v=vs.80).aspx I didn't spot that it was just a CLI thing.
Personally I've not done C++ with the CLI (what's the point when it is so different from proper C++, and if you want to use the CLR, C# is so much nicer).
But still, even if you're doing proper C++ in Visual Studio it's probably best to avoid it. Besides, as you indicate, one should use variables which indicate what they are for, rather than what type they are.
Regards,
Ian.

Espen Harlinn 25-Apr-13 18:42pm

5'ed!

H.Brydon · Accepted Answer · 2013-04-25T05:45:00

Solution 1

Something like this:

C++

void foo()
{
    std::cin >> len;
    int* a = new int[len];  // "array" is a reserved keyword in VC++ as it is used in C++/CLI.
    // use the array "a"...
    delete [] a;  // after allocating with new[] you must use delete[] - the square brackets are important.
}

Posted 25-Apr-13 5:45am

H.Brydon

Updated 25-Apr-13 11:00am

v4

Comments

m.r.m.40 25-Apr-13 11:58am

It worked.
thank you,

Espen Harlinn 25-Apr-13 18:39pm

5'ed!

H.Brydon 25-Apr-13 20:45pm

Thanks again!

Espen Harlinn 25-Apr-13 20:46pm

You're wellcome :-D

C++ declaring array while the program is running

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C++ declaring array while the program is running

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