// std::count 的使用
#include <algorithm>
#include <vector>
#include <iostream>
// A unary predicate for the *_if functions
template<typename elementType>
bool IsEven(const elementType& number) {
// return true if the number is even
return ((number % 2) == 0);
}
int main() {
using namespace std;
// A sample container - vector of integers
vector<int> vecIntegers;
// Inserting sample values
for (int nNum = -9; nNum < 10; ++nNum)
vecIntegers.push_back(nNum);
// Display all elements in the collection
cout << "Elements in our sample collection are: " << endl;
vector<int>::const_iterator iElementLocator;
for (iElementLocator = vecIntegers.begin()
; iElementLocator != vecIntegers.end(); ++iElementLocator)
cout << *iElementLocator << ' ';
cout << endl << endl;
// Determine the total number of elements
cout << "The collection contains '";
cout << vecIntegers.size() << "' elements" << endl;
// Use the count_if algorithm with the unary predicate IsEven:
size_t nNumEvenElements = count_if(vecIntegers.begin(), vecIntegers.end(),
IsEven<int>);
cout << "Number of even elements: " << nNumEvenElements << endl;
cout << "Number of odd elements: ";
cout << vecIntegers.size() - nNumEvenElements << endl;
// Use count to determine the number of '0's in the vector
size_t nNumZeroes = count(vecIntegers.begin(), vecIntegers.end(), 0);
cout << "Number of instances of '0': " << nNumZeroes << endl << endl;
cout << "Searching for an element of value 3 using find: " << endl;
// Find a sample integer '3' in the vector using the 'find' algorithm
vector<int>::iterator iElementFound;
iElementFound = find(vecIntegers.begin() // Start of range
, vecIntegers.end() // End of range
, 3); // Element to find
// Check if find succeeded
if (iElementFound != vecIntegers.end())
cout << "Result: Element found!" << endl << endl;
else
cout << "Result: Element was not found in the collection." << endl;
cout << "Finding the first even number using find_if: " << endl;
// Find the first even number in the collection
vector<int>::iterator iEvenNumber;
iEvenNumber = find_if(vecIntegers.begin() // Start of range
, vecIntegers.end() // End of range
, IsEven<int>); // Unary Predicate
if (iEvenNumber != vecIntegers.end()) {
cout << "Number '" << *iEvenNumber << "' found at position [";
cout << distance(vecIntegers.begin(), iEvenNumber);
cout << "]" << endl;
}
return 0;
}