c++ - 字符转换功能std::isupper()和std::islower()C++ 17

Question

我创建了一个简单的程序来检查用户输入的字母是大写还是小写，然后使用std::isupper()和std::islower()函数将小写字母转换为大写字母，并将大写字母转换为小写字母。在运行代码时，我得到了数字形式的字符转换，而不是预期的大写/小写等效形式。这是为什么？

#include <iostream>

int main()
{
    char letter {};

    std::cout << "Enter a letter:";

    std::cin >> letter;

    if (std::isupper(letter))
    {
        std::cout << "You entered an uppercase letter"
                     "\n"
                     "the lowercase equivalent is:"
                  << std::tolower(letter);
    }

    if (std::islower(letter))    
    {
        std::cout << "You entered a lowercase letter"
                     "\n"
                     "the uppercase equivalent is:"
                  << std::toupper(letter);
    }

    return 0;
}

这是下面的输出示例:

Enter a letter:F
You entered an uppercase letter.
The lowercase equivalent is:102

Enter a letter:f
You entered a lowercase letter.
The uppercase equivalent is:70

Answer 1

if(std::isupper(letter))
{

  std::cout<<"You entered an uppercase letter"<<"\n"

  "the lowercase equivalent is:" << (char)std::tolower(letter);
}

if (std::islower(letter))

{

  std::cout<<"You entered a lowercase letter"<<"\n"

  "the uppercase equivalent is:" << (char)std::toupper(letter);

}

    return 0;

}