How to Convert Strings to Upper/Lower Case in C++

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

int main() {
    std::string text = "Hello, World!";    // Original text

    // Convert to upper case
    for(char &c : text) {                  // Iterate through each character
        c = std::toupper(c);               // Convert character to upper case
    }
    std::cout << "Upper case: " << text << '\n';

    // Convert to lower case
    for(char &c : text) {                  // Iterate through each character
        c = std::tolower(c);               // Convert character to lower case
    }
    std::cout << "Lower case: " << text << '\n';

    return 0;
}

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

int main() {
    std::string text = "Hello, World!";    // Original text

    // Create a copy for upper case
    std::string upper = text;              // Make a copy of original text
    std::transform(upper.begin(),          // Transform each character
                  upper.end(),             // in the string
                  upper.begin(),           // starting from beginning
                  ::toupper);              // using toupper function

    // Create a copy for lower case
    std::string lower = text;              // Make a copy for lower case
    std::transform(lower.begin(),          // Transform each character
                  lower.end(),             // in the string
                  lower.begin(),           // starting from beginning
                  ::tolower);              // using tolower function

    // Print results
    std::cout << "Original: " << text << '\n'
              << "Upper: " << upper << '\n'
              << "Lower: " << lower << '\n';

    return 0;
}

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

// Function to convert string to upper case
std::string toUpper(std::string str) {     // Takes string by value
    std::transform(str.begin(),            // Transform entire string
                  str.end(),               // from beginning to end
                  str.begin(),             // store result from beginning
                  ::toupper);              // using toupper function
    return str;                            // Return modified copy
}

// Function to convert string to lower case
std::string toLower(std::string str) {     // Takes string by value
    std::transform(str.begin(),            // Transform entire string
                  str.end(),               // from beginning to end
                  str.begin(),             // store result from beginning
                  ::tolower);              // using tolower function
    return str;                            // Return modified copy
}

int main() {
    std::string text = "Hello, World!";

    // Using our custom functions
    std::cout << "Original: " << text << '\n'
              << "Upper: " << toUpper(text) << '\n'
              << "Lower: " << toLower(text) << '\n'
              << "Original remains: " << text << '\n';

    return 0;
}

#include <iostream>
#include <string>
#include <algorithm>
#include <locale>

int main() {
    std::string text = "Hello, München!";  // Text with umlaut
    std::locale loc("en_US.UTF-8");        // Create locale object

    std::string upper = text;              // Copy for upper case
    std::transform(upper.begin(),          // Transform string
                  upper.end(),             // from start to end
                  upper.begin(),           // store from beginning
                  [&loc](char c) {         // Lambda for conversion
                      return std::toupper(c, loc);
                  });

    std::cout << "Upper: " << upper << '\n';

    return 0;
}

#include <unicode/unistr.h>
#include <unicode/ustream.h>
#include <unicode/locid.h>
#include <iostream>

int main() {
    // Greek text "Οδυσσέας" (Ulysses)
    const char* text = u8"Οδυσσέας";      // UTF-8 encoded string

    // Convert to ICU's Unicode string
    icu::UnicodeString ustr1(text, "UTF-8");
    icu::UnicodeString ustr2(text, "UTF-8");

    // Greek locale
    icu::Locale greekLocale("el");

    // Convert to upper case with Greek locale
    std::cout << ustr1.toUpper(greekLocale) << "\n";

    // Convert to lower case with Greek locale
    std::cout << ustr2.toLower(greekLocale) << "\n";



    return 0;
}

1. Download the latest ICU4C precompiled binaries for Windows from the ICU GitHub Releases.
2. Extract the downloaded ZIP file to a directory, e.g., C:\icu.
3. Add C:\icu\bin to your system's PATH environment variable.
4. Link the library files (e.g., icuuc.lib, icuin.lib) in your project's build settings.

sudo apt update
sudo apt install libicu-dev

This installs the development headers and libraries required for building projects with ICU support on Debian-based systems (e.g., Ubuntu).

For Fedora/CentOS-based systems, use:

sudo dnf install libicu-devel

Or, if using yum:

sudo yum install libicu-devel

g++ -Wall -std=c++17 main.cpp -I/usr/include -L/usr/lib -licuuc -licuio

This command compiles the program with ICU headers and libraries located in the default system paths. Ensure you have libicu-dev installed.

Explanation of the flags:

• -Wall: Enables all warnings to help identify potential issues.
• -std=c++17: Ensures the compiler uses C++17 features required by ICU.
• -I/usr/include: Specifies the path to ICU header files (default for package manager installations).
• -L/usr/lib: Specifies the path to ICU library files (default for package manager installations).
• -licuuc -licuio: Links the Unicode (`icuuc`) and I/O (`icuio`) libraries from ICU.

If you built ICU from source or installed it in a custom directory, update the include and library paths accordingly. For example:

g++ -Wall -std=c++17 main.cpp -I/path/to/icu/include -L/path/to/icu/lib -licuuc -licuio

Replace /path/to/icu with the actual installation directory of your ICU library, which you can check by doing:

find / -name "icu" 2>/dev/null

icuinfo

This command outputs information about the installed ICU version and its configuration. If it is not available, ensure libicu-dev or libicu-devel is correctly installed.

brew install icu4c

After installation, ensure you link the ICU library during compilation:

g++ -Wall -std=c++17 main.cpp -I/usr/local/opt/icu4c/include -L/usr/local/opt/icu4c/lib -licuuc -licuio

icuinfo

If installed correctly, this command will display detailed information about your ICU library installation.