I wrote a c++ function that uses sequential search to search an array of floats for all all the elements > the key. The function works fine but the problem is it is ver very slow when an array of say 10000 elements is searched since the sequential search algorithm is O(n) .Could any one suggest a fast search algorithm to search a very large array?

#include <stdio.h>
#include <iostream>
#include <stdlib.h>
#include <ctype.h>
#include <cmath>
#include <time.h>
#include <complex>
#include <fstream>
#include <string>
using namespace std;

int find_pos_b(float array[],int size,float key,int *pointer)
int main()
{

float b = 5;//key
float *X;

ifstream file;
file.open("X.txt");
if(file.fail())
{
cout<<"\nError in file opening";
exit(1);
}
int sizex
file>>sizex;
X = new float[++sizex];
for(int i = 0;i<sizex;i++)
{
file>> X[i];
}
X[sizex -1] = 0.0;

file.close();

int matches = 0;
int *pos_b = NULL;

matches = find_pos_b(X,sizex,b,pos_b);//find all the elements >b
pos_b = new int[matches];
if(pos_b == NULL)
{
cout<<"error in memeory allocation. Program exiting.."<<endl;
exit(1);
}
//print result of search
for(int g = 0;g<matches;g++)
{
pos_b[g] = pos_b[g] + 1;
cout<<"pos_b["<<g<<"]="<<pos_b[g]<<endl;
}

delete [] X;
delete [] pos_b;
return 0;
}
//-------------------
//array[]:the array to be searched
//size: the size of the array to be searched
//element:the function returns the indexes of all the elements >= key
//pointer:points to the array holding the result of the search
//the function returns the number of matches found
//--------------------
int find_pos_b(float array[],int size,float key,int *pointer)
{

int i = 0;
int j = 0;
int *p = NULL;//to point to the old array
int *t = NULL;//;= new float[j];
//start the search
while(i<size)
{

if(array[i] >= key)//found
{

p = t;
j++;

t = new int[j];
if(j ==1)
{

t[0] = i;

}
else
{
for(int l = 0;l<j-1;l++)
{
t[l] = p[l];
}
t[j-1] = i;
}

delete [] p;


}
i++ ;
}
pointer = t;

// for(int f = 0;f<j;f++)
// {
// cout<<pointer[f]<<endl;
// }

delete [] t;
t = NULL;
return j;//return the number of matches found
}



thanks