How to use counter in c++

counter in C is an STL container used to store and count different values. It uses integer keys and values, inserts or updates values ​​through the [] operator, and provides operations such as traversing, finding the maximum value, and sorting elements. For example, it can be used to count the number of times a word appears.

Understanding counter in C

counter in C is the standard template library ( STL), is a container class specifically designed to store and count different values. It is similar to an associative container, but focuses more on timing rather than storing data in key-value pairs.

Usage

To use counter, you need to include the <map> header file and instantiate a counter Object:

#include <map>

std::map<int, int> counter;

counter Use integers as keys and integers as values ​​to represent the frequency of each key appearing in the container.

Basic operations

• Insert or update a value: Use the [] operator to insert or update a key value. If the key exists, the value will be updated; otherwise, a new entry will be inserted.
• Get the value: Use the [] operator or the at() method to get the value of the key. If the key does not exist, the at() method will throw an exception and the [] operator will return 0.
• Delete values: Use the erase() method to delete key-value pairs.

Advanced usage

• Traversal: Use begin() and end( ) method gets the iterator of the elements in the container, which can traverse key-value pairs.
• Find the maximum element: Use the max_element() method to find the element with the maximum value.
• Sort: Use the sort() method to sort the elements in a container by value or key.

Example

// 统计单词出现的次数
std::map<std::string, int> word_counter;

// 插入单词及其出现次数
word_counter["hello"]++;
word_counter["world"]++;

// 查找单词出现的次数
int hello_count = word_counter["hello"];

// 遍历单词及其出现次数
for (auto it = word_counter.begin(); it != word_counter.end(); ++it) {
  std::cout << it->first << ": " << it->second << std::endl;
}

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