Manipulating std::string Objects

Count Character Occurrences

How can I count the number of occurrences of a character in a `std::string`?

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Counting the number of occurrences of a character in a std::string can be done using various methods in C++. Here, we'll explore some of the most common techniques.

Using a Loop

A simple way to count occurrences is by using a loop to iterate through each character in the string. For example:

1#include <iostream>
2#include <string>
3
4int main() {
5  std::string Text{"Hello, World!"};
6  char Character{'l'};
7  int Count{0};
8
9  for (const char& c : Text) {
10    if (c == Character) {
11      ++Count;  
12    }
13  }
14
15  std::cout << "Number of '" << Character
16    << "' in \"" << Text << "\": " << Count;
17}

1Number of 'l' in "Hello, World!": 3

Using `std::count`

The <algorithm> header provides the std::count function, which simplifies the process. For example:

1#include <iostream>
2#include <string>
3#include <algorithm>
4
5int main() {
6  std::string Text{"Hello, World!"};
7  char Character{'l'};
8
9  int Count = std::count(
10    Text.begin(), Text.end(), Character
11  );  
12
13  std::cout << "Number of '" << Character
14    << "' in \"" << Text << "\": " << Count;
15}

1Number of 'l' in "Hello, World!": 3

Using a Map for Multiple Characters

If you need to count multiple characters, consider using a map to store the counts. For example:

1#include <iostream>
2#include <string>
3#include <map>
4
5int main() {
6  std::string Text{"Hello, World!"};
7  std::map<char, int> Counts;
8
9  for (const char& c : Text) {
10    ++Counts[c];  
11  }
12
13  for (const auto& Pair : Counts) {
14    std::cout << "Number of '" << Pair.first
15              << "': " << Pair.second << "\n";
16  }
17}

1Number of 'H': 1
2Number of 'e': 1
3Number of 'l': 3
4Number of 'o': 2
5Number of ',': 1
6Number of ' ': 1
7Number of 'W': 1
8Number of 'r': 1
9Number of 'd': 1
10Number of '!': 1

Considerations

Performance: For large strings, using std::count is usually more efficient than a manual loop.
Case Sensitivity: These methods are case-sensitive. To perform a case-insensitive count, you can convert the string to a uniform case before counting.

By using these techniques, you can easily count the number of occurrences of a character in a std::string.

This Question is from the Lesson:

Manipulating `std::string` Objects

A practical guide covering the most useful methods and operators for working with std::string objects and their memory

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6 months ago

This Question is from the Lesson:

Manipulating `std::string` Objects

A practical guide covering the most useful methods and operators for working with std::string objects and their memory

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Count Character Occurrences

How can I count the number of occurrences of a character in a `std::string`?

Using a Loop

Using `std::count`

Using a Map for Multiple Characters

Considerations

Manipulating `std::string` Objects

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How can I iterate through each character of a `std::string` using a range-based for loop?

What is the difference between `reserve()` and `resize()` methods in `std::string`?

How can I convert a `std::string` to a `std::wstring`?

How can I ensure a `std::string` does not exceed a specific length?

How can I reverse the contents of a `std::string`?

How can I trim whitespace from the beginning and end of a `std::string`?

What are the differences between `std::string` and `std::vector<char>`?

Manipulating `std::string` Objects

Professional C++

This course includes:

Professional C++

Count Character Occurrences

How can I count the number of occurrences of a character in a std::string?

Using a Loop

Using std::count

Using a Map for Multiple Characters

Considerations

Manipulating std::string Objects

How can I concatenate two std::string objects in C++?

What is the difference between append() and += operator for strings in C++?

How can I insert a substring into a specific position within a std::string?

How can I replace a substring within a std::string with another string?

How can I iterate through each character of a std::string using a range-based for loop?

What is the difference between reserve() and resize() methods in std::string?

How can I convert a std::string to a std::wstring?

How can I ensure a std::string does not exceed a specific length?

How can I reverse the contents of a std::string?

How can I trim whitespace from the beginning and end of a std::string?

What are the differences between std::string and std::vector<char>?

Manipulating std::string Objects

Professional C++

This course includes:

Professional C++

How can I count the number of occurrences of a character in a `std::string`?

Using `std::count`

Manipulating `std::string` Objects

How can I concatenate two `std::string` objects in C++?

What is the difference between `append()` and `+=` operator for strings in C++?

How can I insert a substring into a specific position within a `std::string`?

How can I replace a substring within a `std::string` with another string?

How can I iterate through each character of a `std::string` using a range-based for loop?

What is the difference between `reserve()` and `resize()` methods in `std::string`?

How can I convert a `std::string` to a `std::wstring`?

How can I ensure a `std::string` does not exceed a specific length?

How can I reverse the contents of a `std::string`?

How can I trim whitespace from the beginning and end of a `std::string`?

What are the differences between `std::string` and `std::vector<char>`?

Manipulating `std::string` Objects