Why is my program pausing after a selection sort function?

Question

I have a simple sorting program being compiled by Dev-C++ 4.9.8.0. I ran the program (yes this compiles) and it simply stops after displaying the line where the vector is displayed for the first time. Note - it does not freeze, it seems to just be taking a pause. In the code, the selection sort comes next so I assume that the error happens there, but there is no error message for me to even figure out what to do!

#include <iostream>
#include <stdlib.h>
#include <vector>
#include <cmath>
#include <ctime>

using namespace std;

void bubbleSort (vector<int>& data)
{
if(data.size() <= 1)
    return;

int flag=1;
int temp;

   for(int i=1; (i<=data.size()) && flag; i++)
   {
       flag=0;
       for(int j=0; (j<data.size()-1); j++)
       {
           if(data[j+1] > data[j])
           {
               temp = data[j];
               data[j] = data[j+1];
               data[j+1] = temp;
               flag=1;
           }
       }
   }
}

void selectionSort(vector<int>& data)
{
    int min, temp, n=data.size();

    for (int i=0; i<n; i++)
    {
        min = i;

        for (int j=i+1; j<n; j++)
        {   
            if (j<min)
            {
                temp=i;
                i=min;
                min=temp;
            }   

        }
    }           
}

int main()
{
    int n;
    vector<int> data;

    cout<<"Vector length?: "<<endl;
    cin>>n;

    srand(time(0));
    for (int i=0; i<n; i++)
    {
        data.push_back(rand()%20+1);
    }

    cout<<"Vector: ";
    for (int i=0; i<data.size(); i++)
    {
        cout<<data[i]<<", ";
    }

    selectionSort(data);

    cout<<"Sorted Vector: ";
    for (int i=0; i<data.size(); i++)
    {
        cout<<data[i]<<", ";
    }

    system("Pause");

    return 0;




}

Answer 1

selectionSort() method has variable 'n' that is completely a random value that happens to be on the stack at that location. You haven't initialized it!

You have a nested loop, which is O(n^2). Say n is 1982734 or some such arbitrarily large number. You are simply looping over 1982734 * 1982734 times. EVENTUALLY it will complete. Why don't you print the value of 'n' inside selectionSort(). Just initialize it with the size of the vector.

As others commented this whole work is in progress.