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## STL algorithm::count() #include <algorithm> Rate Topic: //<![CDATA[ rating = new ipb.rating( 'topic_rate_', { url: 'http://www.dreamincode.net/forums/index.php?app=forums&module=ajax&section=topics&do=rateTopic&t=52509&amp;s=88e37646eccb26aba2234be01cafb4a7&md5check=' + ipb.vars['secure_hash'], cur_rating: 0, rated: 0, allow_rate: 0, multi_rate: 1, show_rate_text: true } ); //]]>

### #1 gabehabe

• GabehabeSwamp

Reputation: 1346
• Posts: 10,918
• Joined: 06-February 08

Posted 19 May 2008 - 12:00 PM

What do I need to know before studying this tutorial?
You should have a knowledge of vectors and vector iterators.

What does the count() algorithm do?
It counts the # of a specified value within a vector

The syntax for the count() algorithm:
int count = count(<where to begin searching>, <where to stop searching>, <value to search for>);

What to include:
#include <iostream> // just to output what's going on
#include <algorithm> // algorithms!
#include <vector> // vector to use algorithms on

using namespace std;

Next, we need to begin our int main () function. I'm gonna assume you know how to do this, and move on.

We need to declare a vector and a vector iterator:
vector <int> myVec; // create a vector called myVec
vector <int> :: iterator it; // create a vector iterator called it

We now need a loop to fill our vector with some values. Let's use some random numbers:
for (int i = 0; i < 9; ++i)
{
int random = rand () % 5; // generate a random number
myVec.push_back(random); // fill the vector with some values
}

Let's print the contents:
cout << "Contents: ";
for (it = myVec.begin(); it != myVec.end(); ++it)
cout << *it << " "; // print the contents of myVec

Next is the count function. Ready? (Take a look at the syntax at the beginning of this tutorial to compare them)
int count_value = count (myVec.begin(), myVec.end(), 4);

Now all we need to do is print our count variable and exit the program:
cout << endl << "Number of 4s stored in vector: " << count_value;

cin.get (); // pause
return EXIT_SUCCESS; // everything went OK

For those of you who learn better by example, here is the complete code:
#include <iostream> // just to output what's going on
#include <algorithm> // algorithms!
#include <vector> // vector to use algorithms on

using namespace std;

int main ()
{
vector <int> myVec; // create a vector called myVec
vector <int> :: iterator it; // create a vector iterator called it

for (int i = 0; i < 9; ++i)
{
int random = rand () % 5; // generate a random number
myVec.push_back(random); // fill the vector with some values
}

cout << "Contents: ";
for (it = myVec.begin(); it != myVec.end(); ++it)
cout << *it << " "; // print the contents of myVec

int count_value = count (myVec.begin(), myVec.end(), 4);

cout << endl << "Number of 4s stored in vector: " << count_value;

cin.get (); // pause
return EXIT_SUCCESS; // everything went OK
}

Is This A Good Question/Topic? 0

## Replies To: STL algorithm::count()

• g+ + -o drink whiskey.cpp

Reputation: 247
• Posts: 13,505
• Joined: 12-July 02

Posted 27 May 2008 - 07:18 AM

This tutorial has been approved, as the information is factually correct. This, with other submissions, however, are really examples of some of the basic features of the algorithm header. Perhaps a more encompassing tutorials grouping several methods together might be beneficial.