Changing a lowercase character to uppercase in c++

Question

Here is the code that i wrote. When i enter a lowercase character such as 'a', it gives me a blank character but afterwards it works well. Can you tell me what i did wrong? Thanks. :)

#include <iostream>
#include <string>
using namespace std;

int main()
{
    char letter;

    cout << "You will be asked to enter a character.";
    cout << "\nIf it is a lowercase character, it will be converted to uppercase.";
    cout << "\n\nEnter a character. Press . to stop: ";

    cin >> letter;

    if(islower(letter))
    {
        letter = isupper(letter);
        cout << letter;
    }

    while(letter != '.')
    {
        cout << "\n\nEnter a character. Press . to stop: ";
        cin >> letter;

        if(islower(letter))
        {
            letter = toupper(letter);
            cout << letter;
        }
    }

    return 0;
}

Solution 1

Because you print a bool value (i.e. false, aka, NUL character here) in the first time.

You should change

letter = isupper(letter);

to

letter = toupper(letter);

Solution 2

Look here:

if(islower(letter))
{
    letter = isupper(letter);
    cout << letter;
}

If the character is lower, then you assigned it the return value of isupper. That should be 0. So you print a null character.

Why don't you just call toupper for every character that you enter? If it's lower it will convert it, if it is already upper it won't do anything.

Solution 3

Generally speaking to convert a lowercase character to an uppercase, you only need to subtract 32 from the lowercase character as this number is the ASCII code difference between uppercase and lowercase characters, e.g., 'a'-'A'=97-67=32.

char c = 'b';
c -= 32; // c is now 'B'
printf("c=%c\n", c);

Another easy way would be to first map the lowercase character to an offset within the range of English alphabets 0-25 i.e. 'a' is index '0' and 'z' is index '25' inclusive and then remap it to an uppercase character.

char c = 'b';
c = c - 'a' + 'A'; // c is now 'B'
printf("c=%c\n", c);