Strange output after reading from a file - c++

Question

Using this code, the following execution yields strange results:
C 100
R
W
The text file's first line defines the number of elements to read from it, and it contains a few values under 15, but every time I run this, the first value in my array is always printed out as 87 (the ASCII value for 'W'). If I change the 'W' functionality to 'X', then the first result in the array is 88.
#include <iostream>
#include <fstream>
using namespace std;
int arrayLength;
class ELEMENT
{
public:
int key;
};
class HEAP
{
public:
int capacity;
int size;
ELEMENT H [];
};
HEAP initialize(int n)
{
HEAP h;
h.capacity = n;
h.size = 0;
return h;
}
void buildHeap(HEAP &h, ELEMENT *a)
{
h.size = arrayLength;
for (int i = 1; i <= arrayLength; i++)
{
h.H[i] = a[i];
}
for (int i = h.size/2; i >= 1; i--)
{
// HEAPIFY HERE
}
}
void printHeap(HEAP &h)
{
cout << "Capacity:\t" << h.capacity << endl;
cout << "Size:\t\t" << h.size << endl;
cout << "|";
for (int i = 1; i <= h.size; i++)
{
cout << " ";
cout << h.H[i].key << " |";
}
cout << endl;
}
int main()
{
char c;
int val;
HEAP h;
while (c != 'S')
{
cin >> c;
switch (c)
{
case 'S':
break;
case 'C':
cin >> val;
h = initialize(val);
break;
case 'W':
printHeap(h);
break;
case 'R':
{
ifstream infile;
infile.open("HEAPinput.txt");
infile >> arrayLength;
ELEMENT* a = new ELEMENT[arrayLength];
for (int i = 1; i <= arrayLength; i++)
infile >> a[i].key;
infile.close();
buildHeap(h, a);
}
break;
}
}
return 0;
}
It is being compiled using g++ on a Unix server.
EDIT:
To clarify:
With a text file with the following contents (space = new line):
12 9 10 11 12 8 7 6 5 4 3 2 1
The output is:
Capacity: 100
Size: 12
| 87 | 10 | 11 | 12 | 8 | 7 | 6 | 5 | 4 | 3 | 2 | 1 |
So it's working except for that first element.

Answer 1

Whatever you think
ELEMENT H [];
is doing, it probably isn't. C++ does not support dynamic arrays - you need to use the std::vector class.
And BTW, C++ by convention uses UPPERCASE to name pre-processor macros and constants. You should use mixed case to name your classes.

Answer 2

In addition to the wrong use of arrays: it would not be a bad idea to make initialize(), buildHeap(), and printHeap() member functions of heap.

Answer 3

It might be because when you say
cout << h.H[i].key <<
H[] is an array of ELEMENTs and the key is an int. If key was a char or cast to char in the cout statement, you'll see the char representation of the int.

Answer 4

What Neil said. Also, arrays in C++ are zero-based. So for example your loop in main():
for (int i = 1; i <= arrayLength; i++)
Should probably be:
for (int i = 0; i < arrayLength; i++)
It could be that the algorithm for binary heap construction just happens to be simpler to implement if you use one-based arrays -- in that case, you'll need to allocate enough space:
ELEMENT* a = new ELEMENT[arrayLength + 1]; // Note the "+ 1"
Currently, the last loop iteration is writing past the end of the array.