I created a simple program to check whether the letter that a user has inputed is either uppercase or lowercase and then convert the lowercase to uppercase and the uppercase to lowercase using the std::isupper()
and std::islower()
funtion. upon running the code I get the character converion in number form instead of the expected uppercase/lowercase equivalent. Why is that?
#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;
}
Here is an example of an output below:
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
std::tolower
and std::toupper
return int
, not char
( due to it's legacy origin from C there are certain requirements due to which int
was chosen, see footnote).
You can cast it back to char to get expected results:
static_cast<char>(std::tolower(letter));
Or you could save the result in a char
variable before (if you need that converted latter elsewhere):
letter = std::tolower(letter);
std::cout << letter;
Note: As noticed by Peter in comment, there are requirements for std::tolower
and std::toupper
that mandate use of type bigger than type actually needed. Quoting it below:
They are also specified as being able to accept and return
EOF
- a value that cannot be represented as a char but can be represented as an int. C++ iostreams (certainly no legacy from C, being specializations of the templatedstd::basic_istream
) have aget()
function with no arguments that reads a character from the stream, and returns an integral type larger than the character type being read. It is part of the machinery of being able to read a single character from a file and deal with error conditions.
You can use std::tolower
and std::toupper
from <locale>
header that return the type you would expect them to return.
Take a look at the examples:
char c {'T'};
std::cout << std::tolower(c, std::locale()) << std::endl; // output: t
and
char c {'t'};
std::cout << std::toupper(c, std::locale()) << std::endl; // output: T
Check live example
You can use std::tolower
and std::toupper
from <cctype>
header that return int
that you need to cast to char
.
Here are the examples:
char c {'T'};
std::cout << static_cast<char>(std::tolower(c)) << std::endl; // output: t
and
char c {'t'};
std::cout << static_cast<char>(std::toupper(c)) << std::endl; // output: T
Check live example
You can also create your own handy helper functions:
char toupper(char c) {
return static_cast<char>(std::toupper(static_cast<unsigned char>(c)));
}
char tolower(char c) {
return static_cast<char>(std::tolower(static_cast<unsigned char>(c)));
}
which you can use like this:
char c1 {'T'};
char c2 {'t'};
std::cout << tolower(c1) << std::endl; // output: t
std::cout << toupper(c2) << std::endl; // output: T
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;
}
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