why is the code not giving out the expected Cipher word?

Im currently working on a project that is supposed to take a key with 26 characters.This key basicaly makes a new alphabet so someone could cipher a word.

For example, if the user inputs the key VCHPRZGJNTLSKFBDQWAXEUYMOI and the word "Hello", the console should answer with "jrssb".Currently, if I input the word "hello", the console prints out "MOAAB" which I don't understand why it does it. ```

#include <cs50.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>



string cipher_word( string key , string text){

char alphabet[] = {'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};

int i = 0 ;
int j = 0 ;
string cipher = text;
while(text[i] != '\0'){//iterates through every char in the string

    while(j < 26){

   char tmpKey;
   char tmpAlphabet;
        tmpKey = key[j];
        tmpAlphabet = alphabet[j];

            if(islower(text[i])){
                tmpAlphabet = tolower(tmpAlphabet);
            }//makes it so the loop can iterate through lowercase letters

       if(text[i] == tmpAlphabet){
          if(islower(cipher[i])){
                cipher[i] = tolower(tmpKey);
            }//is supposed to make the word lowercas if the user inputs a word in lowercase
            cipher[i] = tmpKey;
            }//ciphers the word
            j++;
    }
    j = 0;
    i++;
    }

return cipher;
}

int main(int argc, string argv[])
{

string key = get_string("What is the key? ");
string text = get_string("what text do you want to cipher? ");
string cipher = cipher_word(key,text);

printf("%s\n",cipher);
}

I tried adding the following:

 if(isupper(text[i])){
             text[i] = tolower(text[i]);
         }

It worked but it didn't take into account the uppercase and lowercase letters the user inputs in text. Please explain to me what's wrong with my code?

Solution

In reviewing your code and what was supposed to be the desired output, I took a step back to derive a more generic method of translating/ciphering text. First off, whenever I encounter a question arising for the online tutorials that involve the "CS50" functions, I usually opt to replace the "CS50 specific" functionality within this library set with more generic methods and functions, especially when it comes to string manipulation.

With that in mind, following is a refactored version of your translation function and data entry at the terminal.

Give that a go. Hopefully, that clarifies character matching and translation.

#include <stdio.h>
#include <string.h>
#include <ctype.h>

void cipher_word(char * key, char * text, char * cipher)
{
    char alphabet[] = {'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};

    int i = 0 ;
    int up;

    while(text[i] != '\0')                          // Iterates through every char in the string
    {
        up = isupper(text[i]);                      // Establish whether or not this character is upper case - use for later

        for (int j = 0; j < 26; j++)
        {
            if (toupper(text[i]) == alphabet[j])    // Find the current character in the alphabet for this text character
            {
                cipher[i] = toupper(key[j]);        // Just in case the key was entered in lower case or mixed case
                break;
            }
        }

        if (up == 0)
            cipher[i] = tolower(cipher[i]);         // Make the translated character lower case if the original text character was lower case

        i++;
    }

    return;
}
int main(int argc, char* argv[])
{
    char key[50];                                   // Utilizing standard character array definitions for strings
    char text[20];
    char cipher[20];

    printf("What is the key? ");                    // Utilizing standard prompting for input data
    scanf("%s", key);

    printf("What text do you want to cipher? ");
    scanf("%s", text);

    cipher_word(key, text, cipher);

    printf("%s\n",cipher);

    return 0;
}

The key bits are:

The definition of character arrays (strings)
The check for uppercase or lowercase letters

With those bits of simplification, following was a test at the terminal for a couple of words.

craig@Vera:~/C_Programs/Console/CipherText/bin/Release$ ./CipherText 
What is the key? vchprzgjntlskfbdqwaxeuymoi
What text do you want to cipher? Hello
Jrssb
craig@Vera:~/C_Programs/Console/CipherText/bin/Release$ ./CipherText 
What is the key? vchprzgjntlskfbdqwaxeuymoi
What text do you want to cipher? Chapter
Hjvdxrw

Doing some bench testing, the function performed the desired character replacements to produce the ciphered text.