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Why does isalpha() fail to identify an alphabetic character? (lemm.ee)

submitted 11 months ago* (last edited 11 months ago) by [email protected] to c/[email protected]

8 comments fedilink hide all child comments

This is in C language. When I call rotate() in main, the function returns false for isalpha() even though the string entered for plaintext uses alphabetic characters. Perhaps it's identifying an alphabetic character by its ASCII value ('A' = 65)? I tried to test that out and used (char) with the letter variable in rotate() but it didn't change anything.

PORTION OF MAIN

string plaintext = get_string("plaintext:  ");

    int length = strlen(plaintext);
    char ciphertext[length];

    for (int i = 0; i &lt; length; i++)
    {
        ciphertext[i] = rotate(plaintext[i], key);
    }

ROTATE FUNCTION

char rotate(char letter, int key)
{
    if (isalpha(letter) == true)
    { ...

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[–] [email protected] 3 points 11 months ago

Sorry. It's in C. Updated post. Yes those are titles. I just included the relevant portions rather than the entire code.