C++ Tutorial/STL Algorithms Non modifying sequence operations/for each

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Call custom function in for_each

/* 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>
/* 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);
    }
}
using namespace std;
// function object that adds the value with which it is initialized
template <class T>
class AddValue {
  private:
    T theValue;    // value to add
  public:
    // constructor initializes the value to add
    AddValue (const T& v) : theValue(v) {
    }
    // the function call for the element adds the value
    void operator() (T& elem) const {
        elem += theValue;
    }
};
int main()
{
    vector<int> coll;
    INSERT_ELEMENTS(coll,1,9);
    // add ten to each element
    for_each (coll.begin(), coll.end(),       // range
              AddValue<int>(10));             // operation
    PRINT_ELEMENTS(coll);
    // add value of first element to each element
    for_each (coll.begin(), coll.end(),       // range
              AddValue<int>(*coll.begin()));  // operation
    PRINT_ELEMENTS(coll);
}
11 12 13 14 15 16 17 18 19
22 23 24 25 26 27 28 29 30

The square of every integer in a vector

#include <iostream>
#include <algorithm>
#include <numeric>
#include <vector>
using namespace std;
void outputSquare( int );
int main(){
   const int SIZE = 10;
   int a1[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
   vector< int > v( a1, a1 + SIZE );
   random_shuffle( v.begin(), v.end() );

   cout << "\n\nThe square of every integer in Vector v is:\n";
   for_each( v.begin(), v.end(), outputSquare );
   cout << endl;
   return 0;
}
void outputSquare( int value ) { cout << value * value << " "; }

Use custom function and for_each to calculate mean value

/* 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>
/* 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);
    }
}
using namespace std;
// function object to process the mean value
class MeanValue {
  private:
    long num;    // number of elements
    long sum;    // sum of all element values
  public:
    // constructor
    MeanValue () : num(0), sum(0) {
    }
    // function call
    // - process one more element of the sequence
    void operator() (int elem) {
        num++;          // increment count
        sum += elem;    // add value
    }
    // return mean value (implicit type conversion)
    operator double() {
        return static_cast<double>(sum) / static_cast<double>(num);
    }
};
int main()
{
    vector<int> coll;
    INSERT_ELEMENTS(coll,1,8);
    // process and print mean value
    double mv = for_each (coll.begin(), coll.end(),  // range
                          MeanValue());              // operation
    cout << "mean value: " << mv << endl;
}
mean value: 4.5

Use for_each() algorithm to show elements in a vector and do the summation

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
void show(int i) {
  cout << i << endl;
}
// A running sum.
int summation(int i) {
  static int sum = 0;
  sum += i;
  return sum;
}
int main()
{
  vector<int> v;
  int i;
  for(i=1; i < 11; i++) v.push_back(i);
  for_each(v.begin(), v.end(), show);
  for_each(v.begin(), v.end(), summation);
  
  cout << summation(0);
  return 0;
}

Use for_each function to add first element to each element in the list

/* 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 <list>
#include <algorithm>
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;
}

// function object that adds the value with which it is initialized
class AddValue {
  private:
    int theValue;    // the value to add
  public:
    // constructor initializes the value to add
    AddValue(int v) : theValue(v) {
    }
    // the ""function call"" for the element adds the value
    void operator() (int& elem) const {
        elem += theValue;
    }
};
int main()
{
    list<int> coll;
    // insert elements from 1 to 9
    for (int i=1; i<=9; ++i) {
        coll.push_back(i);
    }
    PRINT_ELEMENTS(coll,"initialized:                ");
    // add value of first element to each element
    for_each (coll.begin(), coll.end(),    // range
              AddValue(*coll.begin()));    // operation
    PRINT_ELEMENTS(coll,"after adding first element: ");
}
initialized:                1 2 3 4 5 6 7 8 9
after adding first element: 2 3 4 5 6 7 8 9 10

Use for_each function to add value for each element

/* 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 <list>
#include <algorithm>
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;
}

// function object that adds the value with which it is initialized
class AddValue {
  private:
    int theValue;    // the value to add
  public:
    // constructor initializes the value to add
    AddValue(int v) : theValue(v) {
    }
    // the ""function call"" for the element adds the value
    void operator() (int& elem) const {
        elem += theValue;
    }
};
int main()
{
    list<int> coll;
    // insert elements from 1 to 9
    for (int i=1; i<=9; ++i) {
        coll.push_back(i);
    }
    PRINT_ELEMENTS(coll,"initialized:                ");
    // add value 10 to each element
    for_each (coll.begin(), coll.end(),    // range
              AddValue(10));               // operation
    PRINT_ELEMENTS(coll,"after adding 10:            ");
}
initialized:                1 2 3 4 5 6 7 8 9
after adding 10:            11 12 13 14 15 16 17 18 19

Use for_each function to print all elements in a vector

/* 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 <algorithm>
using namespace std;
// function that prints the passed argument
void print (int elem)
{
    cout << elem << " ";
}
int main()
{
    vector<int> coll;
    // insert elements from 1 to 9
    for (int i=1; i<=9; ++i) {
        coll.push_back(i);
    }
    // print all elements
    for_each (coll.begin(), coll.end(),    // range
              print);                      // operation
    cout << endl;
}
1 2 3 4 5 6 7 8 9

Use for_each with predicate

#include <iostream>
using std::cout;
using std::endl;
#include <algorithm>
#include <numeric>
#include <vector>
#include <iterator>
void outputSquare( int );
int main()
{
  std::ostream_iterator< int > output( cout, " " );
   int a2[ 10 ] = { 100, 2, 8, 1, 50, 3, 8, 8, 9, 10 };
   std::vector< int > v2( a2, a2 + 10 ); // copy of a2
   cout << "Vector v2 contains: ";
   std::copy( v2.begin(), v2.end(), output );
   // output square of every element in v
   cout << "\n\nThe square of every integer in Vector v is:\n";
   std::for_each( v2.begin(), v2.end(), outputSquare );
   cout << endl;
   return 0;
}
void outputSquare( int value )
{
   cout << value * value << " ";
}
Vector v2 contains: 100 2 8 1 50 3 8 8 9 10
The square of every integer in Vector v is:
10000 4 64 1 2500 9 64 64 81 100

Using for_each to Display the Contents of a Collection

#include <algorithm>
#include <iostream>
#include <vector>
#include <string>
using namespace std;
template <typename elementType>
class DisplayCounter{
private:
    int m_nCount;
public:
    DisplayCounter (){
        m_nCount = 0;
    }
    void operator () (const elementType& element) {
        ++ m_nCount;
        cout << element << " ";
    }
    int GetCount(){
        return m_nCount;
    }
};
int main (){
    vector <int> v;
    for (int nCount = 0; nCount < 10; ++ nCount)
        v.push_back (nCount);
    DisplayCounter<int> mIntResult = for_each ( v.begin (), v.end(), DisplayCounter<int> () );
    cout << mIntResult.GetCount () << endl;

    string str ("this is a test");
    cout << str << endl << endl;
    DisplayCounter<char> mCharResult = for_each (str.begin(), str.end(),DisplayCounter<char> () );
    cout << mCharResult.GetCount () << endl;
    return 0;
}