C++/STL Algorithms Non modifying sequence operations/count
Содержание
- 1 count true value in a vector
- 2 Create a reciprocal function object with transform() and customized function
- 3 Use count function and print elements with value 4
- 4 Use count function to count elements that are greater than value 4
- 5 Use count function to count elements with even value
- 6 Use count on string
- 7 Use count() with vector of boolean value
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;
} /* Sequence: true true false false true false false false false false 3 elements are true.
*/ </source>
Create a reciprocal function object with transform() and customized function
<source lang="cpp">
- include <iostream>
- include <list>
- include <functional>
- include <algorithm>
using namespace std;
class reciprocal: unary_function<double, double> { public:
result_type operator()(argument_type i)
{
return (result_type) 1.0/i;
}
};
int main() {
list<double> l;
int i;
for(i=1; i<10; i++) l.push_back((double)i);
list<double>::iterator p = l.begin();
p = transform(l.begin(), l.end(),l.begin(),reciprocal());
p = l.begin();
while(p != l.end()) {
cout << *p << " ";
p++;
}
return 0;
}
</source>
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;
} /* coll: 1 2 3 4 5 6 7 8 9 number of elements equal to 4: 1
*/ </source>
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;
} /* coll: 1 2 3 4 5 6 7 8 9 number of elements greater than 4: 5
*/
</source>
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;
} /* coll: 1 2 3 4 5 6 7 8 9 number of elements with even value: 4
*/ </source>
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;
} /* There are 4 i"s in str1
*/
</source>
Use count() with vector of boolean value
<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);
}
for(i=0; i<v.size(); i++)
cout << boolalpha << v[i] << endl;
i = count(v.begin(), v.end(), true);
cout << i << " elements are true.\n";
return 0;
}
</source>
