Отсортировать массив пар ключ-значение по ключу

#include "stdafx.h"
#include <iostream>
#include <time.h>
#include <algorithm>
#include <vector>       // std::vector
 
using namespace std;
 
struct KeyValuePair
{
public:
    int Key, Value;
 
    KeyValuePair(int key, int value)
    {
        Key = key;
        Value = value;
    }
 
    KeyValuePair()
    {
        Key = Value = 0;
    }
};
 
 
int Search0 (KeyValuePair[], int, int); 
int Search1 (KeyValuePair[], int, int); 
int Search2 (KeyValuePair[], int, int);
 
int main()
{
    srand ((unsigned) time(0));
    const int n = 12;
    KeyValuePair a[n];
    for (int i = 0; i < n; i++)
    {
        a[i].Key = rand() % (n/2);
        a[i].Value = rand();
    }
 
    cout << "Key\tValue " << endl;
    for (int i = 0; i < n; i++)
    {
        cout << a[i].Key << "\t" << a[i].Value << endl;
    }
    int result0 = Search0(a,n,2);
    cout << result0 << endl;
    int result1 = Search1(a,n,2);
    cout << result1 << endl;
    int result2 = Search2(a,n,2);
    cout << result2 << endl;
    system("pause");
    return 0;
}
 
int Search0 (KeyValuePair a[], int n, int k)
{
    for (int i = 0; i < n; i++) 
        if (k == a[i].Key)      
            return a[i].Value;  
    return -1;
}
 
KeyValuePair* CopyWithExpanding(KeyValuePair a[], int n, int k)
{
    KeyValuePair *result = new KeyValuePair[n+1];
    for (int i = 0; i < n; i++)
        result[i] = a[i];
    result[n].Key = k;
    return result;
}
 
int Search1 (KeyValuePair a[], int n, int k)
{
    KeyValuePair *b = CopyWithExpanding(a,n,k);
    int i = 0;
    for (; b[i].Key != k; i++)
        {}
    int result = i<n? b[i].Value: -1;
    delete(b);
    return result; 
}
 
bool myfunction(int left, int right)
{
    return left < right;
}
 
bool comparator(KeyValuePair left, KeyValuePair right)
{
    return left.Key < right.Key;
}
 
int Search2 (KeyValuePair a[], int n, int k)
{
  KeyValuePair *b = CopyWithExpanding(a,n,k);
  vector<KeyValuePair> myvector2 (b, b+n); 
  cout << "\n\nBEFORE SORT:" << endl;
  for (vector<KeyValuePair>::iterator it=myvector2.begin(); it!=myvector2.end(); ++it)
      cout << "Key = " << (*it).Key << "\tValue = " << (*it).Value << endl;
  cout << '\n';
  sort (myvector2.begin()+4, myvector2.end(), comparator);
  cout << "\n\nAFTER SORT:" << endl;
  for (vector<KeyValuePair>::iterator it=myvector2.begin(); it!=myvector2.end(); ++it)
      cout << "Key = " << (*it).Key << "\tValue = " << (*it).Value << endl;
  cout << '\n';
  return 0;
}