Bubble sort issue - c++

Question

Currently studying software engineering at college (first year) and made a program where the user enters how many entries there will be and then they input the times for each entry and it is sorted in descending order.
The problem I am having is when I enter a large number for the first input it doesn't sort correctly but the rest do. It would be great if someone could help me out with this and sorry for the noob question:P
The entire code:
#include "stdafx.h"
#include <iostream>
using namespace std;
int TotalSize = 0;
void getSpeed(int *CalculationTime, int NoOfCalculations)
{
for (int i = 0; i < NoOfCalculations; i++)
{
cout << "Please enter the speed of calculation " << i + 1 << "(Ms): "; cin >> CalculationTime[i];
}
}
void sort_speeds(int *CalculationTime, int NoOfCalculations)
{
// Sorting speeds in decending order
bool swapped = true;
int i, j = 0;
int temp;
while (swapped)
{
swapped = false;
j++;
for (i = 1; i < NoOfCalculations - j; i++)
{
if (CalculationTime[i] > CalculationTime[i + 1])
{
temp = CalculationTime[i];
CalculationTime[i] = CalculationTime[i + 1];
CalculationTime[i + 1] = temp;
swapped = true;
}
}
}
// Output times decending order
for (int i = 0; i < NoOfCalculations; i++)
{
cout << CalculationTime[i] << "\n";
}
}
int main()
{
// Declaring & Initializing variables
int NoOfCalculations = 0;
int *CalculationTime = new int[NoOfCalculations];
// Getting user input
cout << "How many calculations are there? "; cin >> NoOfCalculations;
getSpeed(CalculationTime, NoOfCalculations);
// Sorting and displaying times
sort_speeds(CalculationTime, NoOfCalculations);
system("pause");
return 0;
}

Answer 1

You've never compare first element of your array with anything - for (i = 1; i < NoOfCalculations - j; i++) should be for (i = 0; i < NoOfCalculations - j; i++)

Answer 2

The issue is for (i = 1; i < NoOfCalculations - j; i++) You are starting at position 1, start at position 0 and it fixes the problem. for (i = 0; i < NoOfCalculations - j; i++)

Answer 3

// Declaring & Initializing variables
int NoOfCalculations = 0;
int *CalculationTime = new int[NoOfCalculations];
// Getting user input
cout << "How many calculations are there? "; cin >> NoOfCalculations;
Bzzzt. You allocate a zero-element array, and then don't reallocate it. I bet if you entered a large enough number for your number of calculations, your program would crash.
Really, you want to be using std::vector, an extremely useful datastructure, the use of which is a bit outside of the scope of this answer. Basically, you can do stuff like this:
std::vector<int> getSpeeds(int NoOfCalculations)
{
std::vector<int> speeds;
for (int i = 0; i < NoOfCalculations; i++)
{
int speed;
std::cout << "Please enter the speed of calculation " << i + 1 << "(Ms): ";
std::cin >> speed;
speeds.push_back(speed);
}
return speeds;
}
You can use the returned vector almost exactly as if it were an array:
std::vector<int> speeds = getSpeeds(10);;
if (CalculationTime[3] > CalculationTime[4])
// do something
Often, in a C++ application, the explicit use of pointers is a sign that you're not using the standard library, and as a result making life much, much harder for yourself.
Oh, and also:
for (i = 1; i < NoOfCalculations - j; i++)
You never look at NoOfCalculations[0] or NoOfCalculations[i - 1], so you never touch the first element.

Answer 4

while (swapped)
{
swapped = false;
j++;
for (i = 0; i < NoOfCalculations - j; i++) //try and start i from 0. I think you are missing the first element to check
{
if (CalculationTime[i] > CalculationTime[i + 1])
{
temp = CalculationTime[i];
CalculationTime[i] = CalculationTime[i + 1];
CalculationTime[i + 1] = temp;
swapped = true;
}
}
}