Simple C++ dynamic array implementation

vec.h

#include <cstdlib>
#include <cstring>

template <typename T> class vec {
private:
  static constexpr size_t INIT_CAP = 1;

  size_t cap;
  size_t count;
  T *data;

public:
  vec() {
    cap = INIT_CAP;
    count = 0;
    data = (T *)malloc(cap * sizeof(T));
  }

  template <class... Ts> vec(Ts... xs) {
    cap = INIT_CAP;
    count = sizeof...(Ts);
    while (cap < count)
      cap *= 2;
    T init[] = {xs...};
    data = (T *)malloc(cap * sizeof(T));
    memcpy(data, init, count * sizeof(T));
  }

  ~vec() { free(data); }

  size_t size() { return count; }

  void push(T item) {
    if (count >= cap) {
      cap *= 2;
      data = (T *)realloc(data, cap * sizeof(T));
    }
    data[count++] = item;
  }

  T pop() { return data[--count]; }

  T &operator[](size_t idx) { return *(data + idx); }

  T *begin() { return data; }
  T *end() { return data + count; }
  const T *cbegin() { return (const T *)data; }
  const T *cend() { return (const T *)(data + count); }
};

// USAGE
#include <cstdio>
#include <vec.h>

int main() {
  vec<int> a = {1, 2, 3, 5};
  for (auto i = 0; i < 5; i++)
    a.push(i * i);

  for (auto i : a)
    printf("%d\n", i);
}