Я бы использовал структуры данных и алгоритмы из std::
:
#include <string>
#include <vector>
#include <algorithm>
#include <iterator>
#include <iostream>
#include <cassert>
#include <sstream>
int main () {
std::string Numbers = "0.3 5.7 9.8 6.2 0.54 6.3";
// If possible, always prefer std::vector to naked array
std::vector<float> v;
// Build an istream that holds the input string
std::istringstream iss(Numbers);
// Iterate over the istream, using >> to grab floats
// and push_back to store them in the vector
std::copy(std::istream_iterator<float>(iss),
std::istream_iterator<float>(),
std::back_inserter(v));
// Put the result on standard out
std::copy(v.begin(), v.end(),
std::ostream_iterator<float>(std::cout, ", "));
std::cout << "\n";
}