warwcat warwcat - 1 month ago 8
C++ Question

c++ vector bubble sort

I use g++ -std=c++11 Sort.cpp to compile my file.

My problem is the bubble sort don't sort.

Maybe I'm passing the vector by value but I don't know is closely my firt time trying work with c++ and I chose use vector library.

My code is:

#include <iostream>
#include <vector>

using namespace std;

void bubbleSort(vector<int> a);

void printVector(vector<int> a);

int main(int argc, char const *argv[])
{
vector<int> a{3,2,6,1};
printVector(a);

bubbleSort(a);
printVector(a);
}

void bubbleSort(vector<int> a)
{
bool swapp = true;
while(swapp)
{
swapp = false;
for (int i = 0; i < a.size()-1; i++)
{
if (a[i]>a[i+1] )
{
a[i] += a[i+1];
a[i+1] = a[i] - a[i+1];
a[i] -=a[i+1];
swapp = true;
}
}
}
}

void printVector(vector<int> a)
{
for (int i=0; i <a.size(); i++)
{
cout<<a[i]<<" ";
}
cout<<endl;
}


In the main I declare a vector type of int's and make the list {3,2,6,1}

After that e call the function
printVector
wich pretends print all numbers of vector on console and call
bubbleSort
function and finally print again.

Answer

You need to pass by reference; by making a copy, you sort a temporary copy, and then that's it; it disappears and the original is still unsorted, because, once again, you sorted only a temporary copy of the entire vector.

So change vector<int> a to vector<int>& a.

Here's the code, fixed:

http://coliru.stacked-crooked.com/a/2f118555f585ccd5

#include <iostream>
#include <vector>

using namespace std;

void bubbleSort(vector<int>& a);

void printVector(vector<int> a);

int main(int argc, char const *argv[])
{
 vector<int> a {3,2,6,1};

 printVector(a);

 bubbleSort(a);

 printVector(a);



}

void bubbleSort(vector<int>& a)
{
      bool swapp = true;
      while(swapp){
        swapp = false;
        for (size_t i = 0; i < a.size()-1; i++) {
            if (a[i]>a[i+1] ){
                a[i] += a[i+1];
                a[i+1] = a[i] - a[i+1];
                a[i] -=a[i+1];
                swapp = true;
            }
        }
    }
}

void printVector(vector<int> a){
    for (size_t i=0;  i <a.size();  i++) {
        cout<<a[i]<<" ";

    }
  cout<<endl;
}