C++ Selection Sort not Sorting Some Values of an Array

There is an easier way to do this by using the swap() function, and using two more functions called, void selectionSort() and void printArray() to make the code look cleaner.

#include <iostream> 
#include <algorithm>

  
void swap(int *xp, int *yp)  
{  
    int temp = *xp;  
    *xp = *yp;  
    *yp = temp;  
}  
  
void selectionSort(int arr[], int n)  
{  
    int i, j, min_idx;  
  
    // One by one move boundary of unsorted subarray  
    for (i = 0; i < n-1; i++)  
    {  
        // Find the minimum element in unsorted array  
        min_idx = i;  
        for (j = i+1; j < n; j++)  
        if (arr[j] < arr[min_idx])  
            min_idx = j;  
  
       
        swap(&arr[min_idx], &arr[i]);  
    }  
}  
  

void printArray(int arr[], int size)  
{  
    int i;  
    for (i=0; i < size; i++)  
        std::cout << arr[i] << " ";  
    std::cout << std::endl;  
}  
  
 
int main()  
{  
    int arr[] = {1, 19, 2, 18, 4, 12, 7, 8, 10, 3, 11, 17, 9}; 
    int n = sizeof(arr)/sizeof(arr[0]);  
    selectionSort(arr, n);  
    std::cout << "The sorted array is: \n";  
    printArray(arr, n);  
    return 0;  
}  

Output:

The sorted array is: 
1 2 3 4 7 8 9 10 11 12 17 18 19 

Another way you could do this is by just strictly using std::swap without the use of pointers. Make sure to include the #include<algorithm> header file for std::swap. You will also need to include #include <iterator> for std::size.

#include <iostream> 
#include <algorithm>
#include <iterator>
 
int main()
{
     int arr[] = {1, 19, 2, 18, 4, 12, 7, 8, 10, 3, 11, 17, 9}; 
    constexpr int length{ static_cast<int>(std::size(arr)) };
    //constexpr means that value of a variable can appear in a constant expression.
 
    // Step through each element of the array
    
    for (int startIndex{ 0 }; startIndex < length - 1; ++startIndex)
    {
        
        int smallestIndex{ startIndex };
 
        // Then look for a smaller element in the rest of the array
        for (int currentIndex{ startIndex + 1 }; currentIndex < length; ++currentIndex)
        {
            if (arr[currentIndex] < arr[smallestIndex])
            
                smallestIndex = currentIndex;
        }
 
        
                // swap our start element with our smallest element 
        std::swap(arr[startIndex], arr[smallestIndex]);
    }
 
    // Now that the whole array is sorted, print it.
    for (int index{ 0 }; index < length; ++index)
        std::cout << arr[index] << ' ';
 
    std::cout << '\n';
 
    return 0;
}

You could also just use std::sort instead. It is in the header file #include<algorithm> which just sorts in ascending order by default. You will also need the header file #include <iterator> for std::size

#include <iostream> 
#include <algorithm>
#include <iterator> 
 
int main()
{
    int arr[] = {1, 19, 2, 18, 4, 12, 7, 8, 10, 3, 11, 17, 9}; 
 
    std::sort(std::begin(arr), std::end(arr));
 
    for (int i{ 0 }; i < static_cast<int>(std::size(arr)); ++i)
        std::cout << array[i] << ' ';
 
    std::cout << '\n';
 
    return 0;
}