Error in the subscript of the array

Question

This is giving me an error that expression a must have a constant value. I cannot understand what is wrong with this method. n is an integer and I am giving it the array size. Can somebody help me to understand this problem?

int fib(int n)
{
const int a = n;
int f[a];
...
}

As it says, it needs to be a _constant_, you’re using a _variable_. C++ doesn’t allow Variable Length Arrays. — Sami Kuhmonen, Jun 09 '18 at 04:42
what's `n` right now? Nobody knows, neither does the compiler. `n` isn't constant — yano, Jun 09 '18 at 04:43
Possible duplicate of [Why aren't variable-length arrays part of the C++ standard?](https://stackoverflow.com/questions/1887097/why-arent-variable-length-arrays-part-of-the-c-standard) — Killzone Kid, Jun 09 '18 at 04:50
@ramsingh In C++, you should be using `std::vector f(a);` for this purpose. — PaulMcKenzie, Jun 09 '18 at 04:52
Possible duplicate of [c++ defining array size with a const variable](https://stackoverflow.com/questions/31090633/c-defining-array-size-with-a-const-variable) — xskxzr, Jun 09 '18 at 06:33

score 1 · Accepted Answer · answered Jun 09 '18 at 04:46

Others have said this already, but essentially the problem is that you are assigning the array a size that is variable and can only be known at runtime of the program. The compiler has to know what size the array is going to be at compile time, so that's a problem and conflicts with the C++ standard. Notably some compilers do have extensions that support this, so that could be your confusion. I would recommend using std::vector instead for anytime you need variable length arrays.

Error in the subscript of the array

1 Answers1