Incorrect result

[onetwo123]

Before I wrote this program with Stooge Sort and means of time was normal.
Now I use Cocktail Sort but time is 0 in CodeBlocks (there I have .cpp and .h files)
Also I have result in online IDE https://ideone.com/GgHXvZ
But why does It not work in CodeBlocks?

#include "cmath"
#include <chrono>
#include <iostream>
#include <algorithm>
#include <vector>
#include <ctime>
#include <cstdlib>
 
using namespace std::chrono;
 
int RandomNumber2() { return (std::rand() % 100); }
void FillVector(std::vector<int>& a) {
    std::srand(unsigned(std::time(0)));
    std::generate(a.begin(), a.end(), RandomNumber2);
    std::cout << "\n\nVector: ";
    for (std::vector<int>::iterator it = a.begin(); it != a.end(); it++) std::cout << *it << " ";
}
 
void CocktailSort(std::vector<int>& a, int n) {
	   bool flag = true;
   int start = 0, end = n-1;
   while(flag){
      flag = false;
      for(int i = start; i<end; i++){
         if(a[i] > a[i+1]){
            std::swap(a[i], a[i+1]);
            flag = true;
         }
      }
      if(!flag){
         break;
      }
      flag = false;
      end--;
      for(int i = end - 1; i >= start; i--){
         if(a[i] > a[i+1]){
            std::swap(a[i], a[i+1]);
            flag = true;
         }
      }
      start++;
   }
}
 
double measureTime(std::vector<int>& a, int n) {
    steady_clock::time_point t1 = steady_clock::now();
    CocktailSort(a, n);
    steady_clock::time_point t2 = steady_clock::now();
    duration<double> time_span = duration_cast<duration<double>>(t2 - t1);
    double mTime = time_span.count();
    std::cout <<  mTime << std::endl;
    return mTime;
}
 
 
void Experiment(std::vector<int> &a, int n) {
    FillVector(a);
    CocktailSort(a, n);
    std::cout << "\n\na. Sorted data: ";
    for (int i{ 0 }; i < n; i++) std::cout << a[i] <<  ' ';
 
    double* times = new double[1000];
 
    for (int i=100; i < 1000; i += 100) {
        std::cout << "\n[" << i << "]" << " ";
        for (int j{1}; j < 10; j+=1) {
            times[j] = measureTime(a, i);
        }
    }
}
 
int main() {
    int n{1000};
    std::vector<int> a(n);
    Experiment(a, n);
 
    return 0;
}

[salem c]

What are you trying to measure?

    FillVector(a);
    CocktailSort(a, n);

You fill with random data, and you sort it.

             times[j] = measureTime(a, i);

Every experiment you time is sorting already sorted data. Depending on the algorithm, this is very quick.

Here's what I saw.

[100] 1.043e-06
8.56e-07
1.021e-06
8.84e-07
5.84e-07
5.65e-07
5.57e-07
5.57e-07
5.55e-07
...
[900] 8.036e-06
7.756e-06
7.727e-06
8.111e-06
7.792e-06
7.904e-06
1.7007e-05
1.7423e-05
1.7041e-05

Depending on the granularity of your clock, things less than a microsecond may as well be instantaneous.

If you want meaningful times then
1. Make sure you're sorting random data.
2. Ideally make it the same random data each time (use a fixed seed)
3. Pick a much bigger value for n.

[onetwo123]

Every experiment you time is sorting already sorted data

Thanks!