Array not changing after sorting function call

Question

When sorting an vector using an implementation of insertion sort, the array I passed as an argument doesn't change as a result.

I've tried this before and can't find my issue, some help would be appreciated.

#include <iostream>
#include <vector>
#include <cstdlib>
#include <algorithm>
using namespace std;
void insertionSort(vector<int> arr);
int main() {
    vector<int> vec;
    const int arrSize = 5;
    for(int i = 0; i < arrSize; i++) {
        vec.push_back(rand() % 10); // 3 6 7 5 3
    }
    for (auto i : vec) cout << i << endl; // 3 6 7 5 3
    insertionSort(vec);
    for (auto i : vec) cout << i << endl; // 3 6 7 5 3
}

void insertionSort(vector<int> arr) {
    for(int i = 0; i < arr.size() - 1; i++) {
        int j = i + 1;
        while(j > 0 && arr[j - 1] > arr[j]) {
            swap(arr[j - 1], arr[j]);
            j--;
        }
    }
    for (auto i : vec) cout << i << endl; // 3 3 5 6 7
}

cadaniluk · Accepted Answer · 2018-05-27 01:08:11Z

3

Arguments are copied by value unless a reference is passed. To modify the object you pass in, use a reference instead.

Pass a vector<int> &arr instead of a mere vector<int> arr. Note the &.

Another way, would be to return the sorted array and assign it to your old, unsorted array.

Some tips:

Prior to rand, call srand to initialize the PRNG with a seed. Since C++11, there is also <random>, which you should favor anyway.
std::endl flushes the stream buffer. '\n' does not, but has the same visual effect. Favor '\n' unless you actually want to flush the stream buffer. Especially in loops, where repeated flushing is superfluous and inefficient.
Use the appropriate size type for STL data structures. For std::vector, this is std::vector<T>::size_type a.k.a. std::size_t. The same as for arrays, BTW. Instead of int, use std::size_t. std::vector::size also returns a std::size_t, not an int.

edited May 27, 2018 at 1:08

answered May 27, 2018 at 1:03

cadaniluk

15.3k2 gold badges45 silver badges71 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Array not changing after sorting function call

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related