Mastering String Manipulation in C++

Lesson Overview

Welcome to an engaging C++ session! Today, we will delve deeper into handling string data in C++. Consider the situations in which you have to analyze text data, like constructing a web scraper or developing a text-based algorithm to interpret the user reviews of a website. All these cases require an efficient handling of strings, which involves analyzing and manipulating them. In this lesson, we will focus on how to traverse strings and perform operations on each character using C++. The objective of this lesson is to become proficient in using C++ loops with a specific emphasis on strings . We will explore the techniques of string indexing and practice character operations using C++ functions.

Working with ASCII Codes in Characters

Characters in C++ can be manipulated using their ASCII values. ASCII (American Standard Code for Information Interchange) is a character encoding standard used to represent text in computers and other devices that use text. Every character has a unique ASCII value. You can convert a character into its ASCII value using a simple cast: C++#include <iostream> int main() { char c = 'A'; int ascii_val = static_cast<int>(c); std::cout << "The ASCII value of " << c << " is: " << ascii_val << std::endl; return 0; } Similarly, you can convert an ASCII value back to its corresponding character: C++#include <iostream> int main() { int ascii_val = 65; char c = static_cast<char>(ascii_val); std::cout << "The character of ASCII value " << ascii_val << " is: " << c << std::endl; return 0; } Manipulating the ASCII value of characters can be quite useful in certain situations. For example, to convert a lowercase letter to uppercase (or vice versa), you could subtract (or add) 32 to the character's ASCII value.

String Indexing Reminder

C++ strings work with a zero-based indexing system. This means that you can access specific characters in a string by using their position. Please note: If you try to access an index that does not exist in your string, C++ will read random memory, which could lead to unpredictable results. Hence, it is recommended always to check the string length before accessing any index. Here's an example: C++#include <iostream> #include <string> int main() { std::string text = "Hello, C++!"; if (text.length() >= 10) { char tenth_char = text[9]; std::cout << "The tenth character is: " << tenth_char << std::endl; } else { std::cout << "The string is too short!" << std::endl; } return 0; }

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Character Operations

Let's now explore the character operations in C++. We have functions like toupper(), tolower(), and type-checking functions that you can use to perform operations on characters. Here are some examples:

The toupper() and tolower() functions are useful when comparing strings irrespective of their case.

C++

#include <iostream>
#include <string>
#include <cctype>

int main() {
    std::string s = "mark";
    for (char& c : s) c = std::toupper(c);
    std::cout << s << std::endl;  // Prints: 'MARK'

    s = "Mark";
    for (char& c : s) c = std::tolower(c);
    std::cout << s << std::endl;  // Prints: 'mark'

    return 0;
}

#include <iostream>
#include <string>
#include <cctype>

int main() {
    std::string s = "mark";
    for (char& c : s) c = std::toupper(c);
    std::cout << s << std::endl;  // Prints: 'MARK'

    s = "Mark";
    for (char& c : s) c = std::tolower(c);
    std::cout << s << std::endl;  // Prints: 'mark'

    return 0;
}

Functions islower() and isupper() can be used to determine whether a character is a lowercase or uppercase letter.

C++

#include <iostream>
#include <cctype>

int main() {
    char a = 'a';
    char b = 'B';
    std::cout << std::boolalpha; // print bool as true/false

    std::cout << "Is " << a << " lowercase? " << static_cast<bool>(islower(a)) << std::endl;  // Prints: true
    std::cout << "Is " << b << " lowercase? " << static_cast<bool>(islower(b)) << std::endl;  // Prints: false

    std::cout << "Is " << a << " uppercase? " << static_cast<bool>(isupper(a)) << std::endl;  // Prints: false
    std::cout << "Is " << b << " uppercase? " << static_cast<bool>(isupper(b)) << std::endl;  // Prints: true

    return 0;
}

#include <iostream>
#include <cctype>

int main() {
    char a = 'a';
    char b = 'B';
    std::cout << std::boolalpha; // print bool as true/false

    std::cout << "Is " << a << " lowercase? " << static_cast<bool>(islower(a)) << std::endl;  // Prints: true
    std::cout << "Is " << b << " lowercase? " << static_cast<bool>(islower(b)) << std::endl;  // Prints: false

    std::cout << "Is " << a << " uppercase? " << static_cast<bool>(isupper(a)) << std::endl;  // Prints: false
    std::cout << "Is " << b << " uppercase? " << static_cast<bool>(isupper(b)) << std::endl;  // Prints: true

    return 0;
}

The isalpha(), isdigit(), and isalnum() functions are useful when you need to check whether the character satisfies a specific condition (is a letter, a digit, or a letter/digit).

C++

#include <iostream>
#include <cctype>

int main() {
    std::cout << std::boolalpha; // print bool as true/false

    std::cout << static_cast<bool>(std::isalpha('C')) << std::endl;  // Prints: true
    std::cout << static_cast<bool>(std::isalpha('+')) << std::endl;  // Prints: false

    std::cout << static_cast<bool>(std::isdigit('9')) << std::endl;  // Prints: true
    std::cout << static_cast<bool>(std::isdigit('D')) << std::endl;  // Prints: false

    std::cout << static_cast<bool>(std::isalnum('6')) << std::endl;  // Prints: true
    std::cout << static_cast<bool>(std::isalnum('k')) << std::endl;  // Prints: true
    std::cout << static_cast<bool>(std::isalnum('?')) << std::endl;  // Prints: false

    return 0;
}