C++ STL vs Pure C

--------------------- C++ STL Solution---------------------------
#include <bits/stdc++.h>

using namespace std;

int main(){

    int t;
    cin >> t;

    while(t--){

        int n , k  , input ;
        cin >> n >> k;

        vector<int> a , b;
        vector< pair<int,int> > v;
        for ( int i = 0; i < n ; i++ ) cin >> input , a.push_back(input);
        for ( int i = 0; i < n ; i++ ) cin >> input , b.push_back(input);
        for ( int i = 0; i < n ; i++ ) v.push_back( {a[i], b[i]} );
        sort ( v.begin(), v.end() );

        for ( int i = 0; i < n ; i++ ){
            if ( v[i].first <= k   ) k += v[i].second;
            else break;
        }

        cout << k << endl;
    }

    return 0;

}


-----------------Pure C Solution-------------------
#include <iostream>

using namespace std;

struct Pair {
    int first;
    int second;
};


void bubbleSort(Pair pair[], int size) {

  for (int step = 0; step < size; step++ ) {

    int swapped = 0;
    for ( int i = 0; i < size-step-1; ++i) {
      if ( pair[i].first > pair[i+1].first ) {
        Pair temp = pair[i];
        pair[i] = pair[i+1];
        pair[i+1] = temp;
        swapped = 1;
      }
    }

    if (swapped == 0) break;
  }

}


int main(){

    int t;
    cin >> t;

    while(t--){

        int n,k;
        cin >> n >> k;
        const size_t size = n;

        int* a = (int*) calloc( size, sizeof(int) );
        int* b = (int*) calloc( size, sizeof(int) );

        for ( int i = 0, input ; i < size ; i++ ) cin >> input, a[i] = input;
        for ( int i = 0, input ; i < size ; i++ ) cin >> input, b[i] = input;

        Pair* pair = (Pair* ) malloc(size*sizeof(Pair));
        for ( int i = 0 ; i < size ; i++ ){
            Pair p = { *(a+i), *(b+i) };
            pair[i] = p;
        }
        free(a);
        free(b);

        bubbleSort(pair, size);

        for ( int i = 0; i < size ; i++ ){
            if ( pair[i].first <= k ) k += pair[i].second;
            else break;
        }

        cout << k << endl;
        free(pair);
    }

    return 0;
}