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Generic Algorithms

The library provides a set of algorithms, most of which are independent of any particular container type. Those algorithms implement common functions such as sorting and searching. Most of the algorithms are defined in the algorithm header. In general, the algorithms do not work directly on a container. Instead, they operate by traversing a range of elements bounded by two operators.

For example: Lest’s suppose we have a vector of int and we want to know if that vector holds a particular value.

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{
  int value=36;

  vector<int> numbers = {2,12,18,36,40,58};
  auto result = find(numbers.cbegin(), numbers.cend() ,value);
  cout << (result == numbers.cend() ? "is not present" : "found!") << endl;

}

Because find operates in terms of iterators, we can use the same find function to look for values in any type of container. For example, because pointers act like iterators, we can use find in an array.

#include <iostream>
#include <assert.h>
#include <algorithm>

using namespace std;

int main()
{
  int value=36;

  int numbers[] = {2,12,18,36,40,58};
  auto result = find(begin(numbers), end(numbers) ,value);
  assert(*result == 36);

}

Read-Only algorithms

A numner of the algorithms read, but never write to, one of those is accumulate, which is defined in the numeric header.

#include <iostream>
#include <vector>
#include <assert.h>
#include <algorithm>

using namespace std;

int main()
{

  vector<int> numbers = {2,12,18,36,40,58};
  int sum = accumulate(numbers.cbegin(), numbers.cend(), 0);
  assert(sum == 166);

}

sets sum equal to the sum of the elements in the vector, using 0 as starting point of summation.

Algorithms that write container elements

Some algorithms assign new values to the elements in a sequence.

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

int main()
{

  vector<int> numbers = {2,12,18,36,40,58};
  fill(numbers.begin(), numbers.begin() + numbers.size()/2, 0);

  for(int it: numbers){
    cout << it << endl;
  }

}

Output:

0
0
0
36
40
58

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