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 here int top; public: Stack(){ this->cap=5; this->top=-1; }; The indicated line has these errors:
Multiple markers at this line - invalid use of 'this' at top level - array bound is not an integer constant before ']' token What am I doing wrong?
In C++, the size of an array must be a constant known at compile-time. You'll get an error if that isn't the case.
Here, you have
int elements[this->cap]; Notice that this->cap isn't a constant known at compile-time, since it depends on how big cap is.
If you want to have a variably-sized array whose size is determined later on, consider using std::vector, which can be resized at runtime.
Hope this helps!
You cannot use this in the declaration like that. this is a constant pointer passed to non-static methods in your class. It does not exist outside of that scope.
Such array declarations need constant values/expressions for the size. You don't want that, you want a dynamicly sized container. The solution is to use a std::vector.
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<int> consider using a pointer implementation.
#include <algorithm> 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); } }; Change
int elements[this->cap]; to
int* elements=new int[cap]