count_if()

#include <algorithm>

difference_type count_if (In first, In last, Pred pred) 
difference_type count_if (Exec pol, In first, In last, Pred pred) 
 
difference_type ranges::count_if (Range r, Pred pred, Proj proj = {}) 
difference_type ranges::count_if (In first, In last, Pred pred, Proj proj = {}) 

Liefert die Anzahl der Elemente e des Bereiches [first,last), auf die das Prädikat pred(proj(e)) zutrifft.

Rückgabewert: Anzahl der Iteratoren i im Bereich [first,last), für die pred(proj(*i)) != false ist.

count().

count_if.cpp

#include <algorithm>
#include <string>
#include <iostream>
 
bool ist_Vokal(char c)
{
  const char vokale[] = "aeiou";
  return std::binary_search(vokale, vokale+5, std::tolower(c));
}
 
int main()
{
  std::string s = "Hallo Welt";
  std::cout << std::count_if(begin(s), end(s), ist_Vokal) << '\n';
}