Introsort implementation in C++

introsort.cpp

#include <math.h>
#include <algorithm>
#include <iostream>
using namespace std; 
void introsort_r(int a[], int first, int last, int depth);
void _introsort(int a[], int n);
int _partition(int a[], int first, int last);
void _insertion(int a[], int n);
void _swap(int *a, int *b);
void _doheap(int a[], int begin, int end);
void _heapsort(int a[], int begin, int end);
bool _isSorted(int a[], int end);
 
void introsort_r(int a[], int first, int last, int depth){
  while(last - first > 0 ) {
		if(depth=0)
			_heapsort(&a[first], first,  last-first+1 );
		else {
			int pivot;
			if( _isSorted(a, last))
				break;
			pivot = _partition(a, first, last);
			introsort_r(a, pivot+1, last, depth-1);
			last = pivot -1;
		}
	}
}
 
void _introsort(int a[], int n){
	introsort_r ( a, 0, n-1, (int(2*log(double(n)))));
	_insertion(a, n);
}
 
int _partition ( int a[], int first, int last){
	int pivot, mid = (first+last)/2;
 
	pivot = a[first] > a[mid]  ? first : mid;
 
	if( a[pivot] > a[last])
		pivot = last;
 
	_swap( &a[pivot], &a[first] );
	pivot = first;
 
	while ( first < last ){
		if ( a[first] <= a[last] )
			_swap( &a[pivot++], &a[first] );
		++first;
	}
 
	_swap (&a[pivot], &a[last]);
	return pivot;
}
 
void _insertion ( int a[], int n ) {
	int i;
	for ( i = 1; i < n; i++ ) {
		int j, save = a[i];
		for ( j = i; j >= 1 && a[j - 1] > save; j-- )
			a[j] = a[j - 1];
		a[j] = save;
	}
}
 
void _swap(int *a, int *b){
	int save = *a;
	*a = *b;
	*b = save;
}
void _doheap(int a[], int begin, int end ){
	int save = a[begin];
	while (begin <= end /2) {
		int k = 2* begin;
		while ( k < end && a[k] <a[k+1])
			++k;
		if( save >= a[k])
			break;
		a[begin] = a[k];
		begin = k;
	}
	a[begin] = save;
}
 
void _heapsort(int a[], int begin, int end ){
	int i;
	for(int i = (end-1) / 2; i >= begin; i--){
		_doheap( a, i , end-1);
	}
	for( i=end-1; i>begin; i --){
		_swap( &a[i], &a[begin]);
		_doheap(a, begin, i-1);
		}
}
bool _isSorted(int a[], int end){
	for(int i=0; i<end; i++){
		if(a[i] > a[i+1]){
			return false;
		} else {
			return true;
		}
	}
	return true;
}
int main()
{
	int arrayNum[50],t; 
	cout<<"Enter Number of Elements:";
	cin>>t;
	for(int y = 0; y<t; y++)
	{
		cin>>arrayNum[y];
	}
	_introsort(arrayNum, t);
	for(int x = 0; x<t; x++)
	{
		std::cout << x << ":" << arrayNum[x] << std::endl;
	}
	cin.get();
	return 0;
}