Getting sigabrt error in heapsort program - c++

Question

I am getting sigabrt error as given below for the given heapsort program. I am new to programming so I apologize for silly mistakes.
error : Abort signal from abort(3) (SIGABRT)
The major parts of the code are as follows
heapify - a program to make a heap out of the given array
heapsort - a function which sorts the array according to a heap and saves the result in the array
main - the driver function
#include <iostream>
#include <math.h>
using namespace std;
void swapper (int first, int second) {
int temp;
temp = second;
second = first;
first = temp;
}
void heapify (int a[], int size) {
for(int i = 0; i < (size/2) ; i++) {
int left = 2*i;
int right = 2*i + 1;
if (a[i] < a[left]) {
swap(a[i], a[left]);
}
else if (a[i] < a[right]) {
swap(a[i],a[right]);
}
}
}
void heapsort(int a[], int size){
int treesize = size;
int i = size;
heapify(a,size);
while (treesize > 0) {
cout << " \t " << a[i];
swap(a[i],a[0]);
i --;
treesize--;
heapify(a, treesize);
}
cout <<"\n";
for(int i = 0; i < size; i++) {
cout <<"\t"<<a[i];
}
}
int main() {
// your code goes here
int a[] = {10,1,2,11,4,57,12,13,44,14,6,7,9,8,15,16,17,98};
int arrsize= sizeof(a)/(sizeof(a[0]));
int pos;
int ele = 7;
heapsort(a,arrsize);
for (int i = 0; i < arrsize; i++){
cout <<"\n "<<a[i];
cout<<"\n"<<arrsize;
}
return 0;
}

Answer 1

I'm not sure about the correctness of the rest of the program, but the reason why you're getting the exception is because you're accessing memory out of bounds. You call heapsort with the array size like this:
heapsort(a, arrsize);
And then you set treesize and i to that size:
int treesize = size;
int i = size;
And then in those lines:
cout << " \t " << a[i];
swap(a[i], a[0]);
i is still equal to arraysize. But it can at most be arraysize-1. This causes undefined behavior when you print a[i], and even worse, undefined behavior in the following line that modifies values outside of the array. On my machine, the former prints rubbish values and the latter causes stack corruption. Instead, you should set those values like this:
int treesize = size-1;
int i = size-1;
This fixes the print and the exception.