C++ Tutorial/STL Algorithms Non modifying sequence operations/count
Содержание
count true value in a vector
<source lang="cpp">#include <iostream>
- include <vector>
- include <cstdlib>
- include <algorithm>
using namespace std; int main() {
vector<bool> v; unsigned int i; for(i=0; i < 10; i++) { if(rand() 2) v.push_back(true); else v.push_back(false); } cout << "Sequence:\n"; for(i=0; i<v.size(); i++) cout << boolalpha << v[i] << " "; cout << endl; i = count(v.begin(), v.end(), true); cout << i << " elements are true.\n"; return 0;
}</source>
Sequence: true true false false true false false false false false 3 elements are true.
Use count function and print elements with value 4
<source lang="cpp">/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference" * by Nicolai M. Josuttis, Addison-Wesley, 1999 * * (C) Copyright Nicolai M. Josuttis 1999. * Permission to copy, use, modify, sell and distribute this software * is granted provided this copyright notice appears in all copies. * This software is provided "as is" without express or implied * warranty, and with no claim as to its suitability for any purpose. */
- include <iostream>
- include <vector>
- include <deque>
- include <list>
- include <set>
- include <map>
- include <string>
- include <algorithm>
- include <iterator>
- include <functional>
- include <numeric>
using namespace std; /* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by * - all elements of the collection coll * - separated by spaces */
template <class T> inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="") {
typename T::const_iterator pos; std::cout << optcstr; for (pos=coll.begin(); pos!=coll.end(); ++pos) { std::cout << *pos << " "; } std::cout << std::endl;
} /* INSERT_ELEMENTS (collection, first, last)
* - fill values from first to last into the collection * - NOTE: NO half-open range */
template <class T> inline void INSERT_ELEMENTS (T& coll, int first, int last) {
for (int i=first; i<=last; ++i) { coll.insert(coll.end(),i); }
}
int main()
{
vector<int> coll; int num; INSERT_ELEMENTS(coll,1,9); PRINT_ELEMENTS(coll,"coll: "); // count and print elements with value 4 num = count (coll.begin(), coll.end(), // range 4); // value cout << "number of elements equal to 4: " << num << endl;
}</source>
coll: 1 2 3 4 5 6 7 8 9 number of elements equal to 4: 1
Use count function to count elements that are greater than value 4
<source lang="cpp">/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference" * by Nicolai M. Josuttis, Addison-Wesley, 1999 * * (C) Copyright Nicolai M. Josuttis 1999. * Permission to copy, use, modify, sell and distribute this software * is granted provided this copyright notice appears in all copies. * This software is provided "as is" without express or implied * warranty, and with no claim as to its suitability for any purpose. */
- include <iostream>
- include <vector>
- include <deque>
- include <list>
- include <set>
- include <map>
- include <string>
- include <algorithm>
- include <iterator>
- include <functional>
- include <numeric>
using namespace std; /* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by * - all elements of the collection coll * - separated by spaces */
template <class T> inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="") {
typename T::const_iterator pos; std::cout << optcstr; for (pos=coll.begin(); pos!=coll.end(); ++pos) { std::cout << *pos << " "; } std::cout << std::endl;
} /* INSERT_ELEMENTS (collection, first, last)
* - fill values from first to last into the collection * - NOTE: NO half-open range */
template <class T> inline void INSERT_ELEMENTS (T& coll, int first, int last) {
for (int i=first; i<=last; ++i) { coll.insert(coll.end(),i); }
}
bool isEven (int elem) {
return elem 2 == 0;
}
int main() {
vector<int> coll; int num; INSERT_ELEMENTS(coll,1,9); PRINT_ELEMENTS(coll,"coll: "); // count elements that are greater than value 4 num = count_if (coll.begin(), coll.end(), // range bind2nd(greater<int>(),4)); // criterion cout << "number of elements greater than 4: " << num << endl;
}</source>
coll: 1 2 3 4 5 6 7 8 9 number of elements greater than 4: 5
Use count function to count elements with even value
<source lang="cpp">/* The following code example is taken from the book
* "The C++ Standard Library - A Tutorial and Reference" * by Nicolai M. Josuttis, Addison-Wesley, 1999 * * (C) Copyright Nicolai M. Josuttis 1999. * Permission to copy, use, modify, sell and distribute this software * is granted provided this copyright notice appears in all copies. * This software is provided "as is" without express or implied * warranty, and with no claim as to its suitability for any purpose. */
- include <iostream>
- include <vector>
- include <deque>
- include <list>
- include <set>
- include <map>
- include <string>
- include <algorithm>
- include <iterator>
- include <functional>
- include <numeric>
using namespace std; /* PRINT_ELEMENTS()
* - prints optional C-string optcstr followed by * - all elements of the collection coll * - separated by spaces */
template <class T> inline void PRINT_ELEMENTS (const T& coll, const char* optcstr="") {
typename T::const_iterator pos; std::cout << optcstr; for (pos=coll.begin(); pos!=coll.end(); ++pos) { std::cout << *pos << " "; } std::cout << std::endl;
} /* INSERT_ELEMENTS (collection, first, last)
* - fill values from first to last into the collection * - NOTE: NO half-open range */
template <class T> inline void INSERT_ELEMENTS (T& coll, int first, int last) {
for (int i=first; i<=last; ++i) { coll.insert(coll.end(),i); }
}
bool isEven (int elem) {
return elem 2 == 0;
}
int main() {
vector<int> coll; int num; INSERT_ELEMENTS(coll,1,9); PRINT_ELEMENTS(coll,"coll: "); // count elements with even value num = count_if (coll.begin(), coll.end(), // range isEven); // criterion cout << "number of elements with even value: " << num << endl;
}</source>
coll: 1 2 3 4 5 6 7 8 9 number of elements with even value: 4
Use count on string
<source lang="cpp">#include <iostream>
- include <string>
- include <algorithm>
using namespace std; int main() {
string str1("Strings handling is easy in C++"); string::iterator p; unsigned int i; // use the count() algorithm i = count(str1.begin(), str1.end(), "i"); cout << "There are " << i << " i"s in str1\n"; return 0;
}</source>
There are 4 i"s in str1