C++ keyword: continue - cppreference.com

#include <iostream>
#include <string>

[[nodiscard]] constexpr auto get_digits(const std::string& string) noexcept
{
    std::string digits{};

    for (const auto& character: string)
    {
        if (character < '0' || character > '9') [[likely]]
            continue; // conditionally skips the following statement
        digits += character;
    }
    
    return digits;
}

int main() noexcept
{
    std::cout << get_digits("H3LL0, W0RLD!");
}