Getting error “array bound is not an integer constant before ']' token”

Question

I am trying to implement a stack using an array but I receive an error.

class Stack{
private:
    int cap;
    int elements[this->cap]; // <--- Errors          


        

Answer 1

Since other have already explained the cause of this issue, here is a possible solution to resolve it. Since it seems you may not know the array size at compile time and the assignment may restrict the use of std::vector consider using a pointer implementation.

#include 

class Stack{
private:
    int cap;
    int* elements; // use a pointer
    int top;
public:
    Stack(){
        this->cap=5;
        this->top=-1;
        elements = new int[this->cap];
    }

    Stack(const Stack& s) 
         : cap(s.cap) , top(s.top), elements(NULL)
    {
         if(cap > 0) {
             elements = new int[cap];
         }

         std::copy(s.elements , s.elements + cap, elements );
    }

    Stack& operator=(Stack s) {
         swap(s, *this);
         return  *this;
    }

    ~Stack() {delete [] elements;}

    friend void swap(Stack& first, Stack& second)
    {
        using std::swap; 
        swap(first.top, second.top);
        swap(first.cap, second.cap);
        swap(first.elements, second.elements);
    }
};