Make a char lowercase using C++

My question is very short.

However, the answer is very long. Let's start!

Short answer.

You can use std::tolowerlike this:

   *key = std::tolower(*key);
// ^------ Des-referencia el puntero.

Long answer.

We have two versions of std::tolower:

• In the header <cctype>:

  int tolower( int ch );
  

• In the header <locale>:

  template< class charT >
  charT tolower( charT ch, const std::locale& loc ) {
      return std::use_facet<std::ctype<charT>>(loc).tolower(ch);
  }
  

The header version <cctype>belongs to the C libraries while the header version <locale>belongs to the C++ libraries. If you are programming in C++ you should use<locale> .

In addition to what was said in the previous paragraph, why is the version better <locale>than the version of <cctype>?:

• The C version converts character ( char) to integer (receives a int) and returns an integer (returns int) that will have to be converted back to character ( char).
• The C++ version is a template that takes a generic character type ( charT) and converts it to lowercase using the language locale; so not only does it take into account all character types ( char, wchar_t, char16_tand char32_t) without doing data transformations, it also takes into account the language they are written in!

So to lowercase a character using the configured language setting you would do:

// Usa el idioma actual -----v
   *key = std::tolower(*key, std::locale(""));
// ^------ Des-referencia el puntero.

Other things to keep in mind.

Doing this is terrible!

char key[16];
key = "A";

You request 16 characters and then you re-assign the pointer, that is not allowed in C++ and that is why you get the error incompatible types in assignment of 'int' to 'char [16]', to create one keythat contains "A"you must do this:

char key[16] = "A";

Considering your question -> Lowercase a char using C++, not going into details already mentioned by eferion for example and shown by PaperBirdMaster in his type error question is not assignable, you can use the difference that exists in the ASCII table

in between the characters in uppercase and the same but in lowercase , the lowercase are, so to speak, 32 positions away from the same character in uppercase, knowing this you can do something like the following (simple example on a char) :

#include <iostream>
using namespace std;

int main() {
    // your code goes here
    char key = 'A';

    char test = key + 32;

    std::cout << key << std::endl;
    std::cout << test << std::endl;

    std::cout << (key += 32) << std::endl;
    return 0;
}

stdout:

A
a
a

TestIdeone

PS: To put a lowercase letter in uppercase, you would only have to use -= 32for example instead of += 32.