Количество чисел в строке

#include <iostream>
#include <string>
using namespace std;

int main()
{
  string str;
  cout << "Enter string:\n";
  getline (cin, str);
  int countOfNums = 0;
  for (int i = 0; i < str.length(); i++) {
      if (((int)str[i] >= (int)'0') && ((int)str[i] <= (int)'9')) {
          countOfNums++;
      }
  }
  cout << countOfNums << endl;
  system("pause");
}