StringBuilder Class in C++ not working properly - c++

Question

I'm working on an assignment to create a class called StringBuilder that is used for fast string concatenation. I'm supposed to store strings in a dynamic array and have methods such as Append(string) which adds a new string to the dynamic array. The method I'm currently struggling with is GetString() that creates a single string on the heap that is the length of all the strings in the dynamic array that have been added thus far.
the code I have so far is:
okay my main problem is my GetString() function prints out hello over and over again until I force quit the program in Xcode. I don't understand what inside that method is making that happen.
My header file:
#pragma once
#include <string>
using namespace std;
class StringBuilder
{
public:
StringBuilder();
//~StringBuilder();
void GetString();
void AppendAll(string*, int);
void Length();
void Clear();
void Append(string userString);
void DoubleArray(string*& allWords, int newCapacity);
private:
string* p_array;
int capacity = 5;
};
my .cpp file :
#include "StringBuilder.hpp"
#include <iostream>
#include <string>
using namespace std;
----------
void StringBuilder::Append(string userString)
{
int nextWordPosition = 0;
for(int i=0; i < capacity ; i++)
{
p_array[i] = userString;
cout << p_array[i] << endl;
nextWordPosition +=1;
if(capacity == nextWordPosition)
{
capacity *=2;
DoubleArray(p_array, capacity * 2);
}
}
nextWordPosition++;
}
void StringBuilder::DoubleArray(string*& allWords, int newCapacity)
{
string* p_temp = new string[newCapacity];
for(int i =0; i < newCapacity / 2; i++)
{
p_temp[i] = allWords[i];
}
delete[] allWords;
allWords = p_temp;
}
void StringBuilder:: GetString()
{
for(int i=0; i < capacity ; i++)
{
cout << p_array[i]<< endl;
}
}
my main.cpp file :
#include <iostream>
#include <string>
#include "StringBuilder.hpp"
using namespace std;
int main()
{
string testString = "hello";
string test = "world!";
StringBuilder Builder1;
Builder1.Append(testString);
Builder1.Append(test);
Builder1.GetString();
return 0;
}