C++/STL Algorithms Helper/not1

  
#include <functional>
#include <algorithm>
#include <cctype>
#include <string>
#include <iostream>
using namespace std;
bool isNumber(const string& str)
{
  string::const_iterator it = find_if(str.begin(), str.end(), not1(ptr_fun(::isdigit)));
  return (it == str.end());
}
int main(int argc, char** argv)
{
  cout << isNumber("12345") << endl;
  cout << isNumber("hello") << endl;
  cout << isNumber("1234a") << endl;
  return (0);
}