CODEWITHSUNDEEP
c++arraysvisual-c++dynamic
Raj
Raj

Reputation: 674

Creating dynamic sized array using MSVC C++ compiler

I am using visual studio 2013 express and MSVC compiler.

I get an error on executing the following lines of code.

#include<iostream>
using namespace std;
int main()
{
     int n;
     cin>>n;
     int a[n];
     return 0;
}

It says expression must have a constant value on the line on which I declare array a. I searched and found this c++ array - expression must have a constant value

It says you need to turn on a compiler option to allow it. How do I set that option in Visual studio express?

Upvotes: 1

Views: 2242

Answers (2)

Oblivion
Oblivion

Reputation: 7374

You can use pointers 

int*a = new int [n];

You have to delete before going out of your a's scope:

delete[] a;

But better use vector:

vector<int> a(n);

You can also use llvm smallvector which is optimized for small arrays with no heap allocation if the size was small 

llvm::SmallVector<int, 5> smallVector;
 for(int i = 0; i < 5; i++) { 
    smallVector.push_back(i); } // No heap allocations have been performed up to this point.
     smallVector.push_back(6); // heap allocation now

But keep in mind the compiler will decide where to allocate. Smallvector

Upvotes: 4

bahij zeineh
bahij zeineh

Reputation: 228

try the following:

#include<iostream>
using namespace std;
int main()
{
    int n;
    cin >> n;
    int *a=new int[n];
    delete[] a;
    return 0;
}

the way your doing it it gets allocated on the stack and for that it has to be constant whereas this way its on the heap and it can be whatever value.

i dont think there is a compiler option to change that

Upvotes: 1

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