CS50 (cs50x) pset2 Substitution Solution 2020

substitution.c

#include <stdio.h>
#include <cs50.h> // to get plain text
#include <string.h> // for strlen()
#include <ctype.h> // for string operation upper, lower

void Do_substitute(); // for further substitute
void alpha_arr_val(char pos, string key);
// to get the alphabet array value of each plain text element (ex:plaintext = h|alphabet array = 8 {a=0, b=1 .....z=26})

int main(int argc, string argv[])
{
    if (argc == 2) // number of commands in terminal
    {
        if (strlen(argv[1]) == 26)
        {
            for (int i = 0; i < strlen(argv[1]) ; i++) // checking each element of string
            {
    
                if (! isalpha(argv[1][i])) // if contain non-alphabet
                {
                    printf("Key must contain 26 characters.\n");
                    return 1;
                }
    
                for (int j = i + 1 ; j < strlen(argv[1]) ; j++) // checking to the next element of arg[i]
                {
    
                    if (toupper(argv[1][j]) == toupper(argv[1][i])) // checking repeated element
                    {
                        printf("Key must not contain repeated alphabets.\n");
                        return 1;
                    }
                }
            }
            
            Do_substitute(argv[1]);
            
        }
        else
        {
            printf("Key must contain 26 characters.\n");
            return 1;   
        }
        
    }
    else
    {
        printf("Usage: ./substitution key\n");
        return 1;
    }

    return 0;
}


void Do_substitute(string key)
{
    string p = get_string("plaintext: ");

    printf("ciphertext: ");

    for (int i = 0; i < strlen(p); i++)
    {
        if (isalpha(p[i])) // checking p[i] is alphabet
        {
            char x = p[i];
            if (islower(p[i]))
            {
                alpha_arr_val(tolower(x), key); // passing p[i] in lower-case
            }
            else
            {
                alpha_arr_val(toupper(x), key); // passing p[i] in UPPER-CASE
            }


        }
        else
        {
            printf("%c", p[i]); // print the element as it is (such as space | , | special characters | ? | etc...)
        }
    }

    printf("\n");

}
void alpha_arr_val(char pos, string key) // passing p[i] and upper/lower(alpha array)
{
    string alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"; // alphabet array

    for (int i = 0; i < strlen(alpha); i++) // accessing each element in alpha array
    {
        if (islower(pos)) // p[i] is lower
        {
            if (pos == tolower(alpha[i]))
            {
                printf("%c", tolower(key[i]));
            }
        }
        else // for UPPERCASE // p[i] is upper
        {
            if (pos == toupper(alpha[i]))
            {
                printf("%c", toupper(key[i]));
            }
        }
    }
}

#line 6 you might consider removing the check_key () function on line 6, seems redundant.
#line 61 you couldmerge the printf("ciphetext: ") statement on line 61 and merged it with that on line 81.

#line 6 you might consider removing the check_key () function on line 6, seems redundant. #line 61 you couldmerge the printf("ciphetext: ") statement on line 61 and merged it with that on line 81.

Dear @Tomi-3-0 ,
Thankyou for your suggestion on #line 6 , the checkey() function was declared but never initialized, I've updated the changes.

#line 61, if we try to merge the printf's on line 61 and line 81, since it is written inside the loop we see "ciphertext : " repeatedly which may be not look pleasing as per viewing experience. But I encourage you to try to merge the lines as per your convenience. :)

Why does it return 1?

return 1 means interrupting the execution of a code and aborting the program. Please notice line no 21,30, 41,48 these printf statements are indicating error, and to terminate the program so that it will not move further we use return 1 (because the main function is initialized with int return type).
return 0 for successfully exiting from the program.

this was posted like a billion years ago

…

On Mon, Nov 13, 2023 at 12:57 PM khoaoaoaoa ***@***.***> wrote: ***@***.**** commented on this gist. ------------------------------ for me, it is kinda simple `#include <cs50.h> #include <ctype.h> #include <stdio.h> #include <string.h> int check_CLIargs(int argc, string argv[]); string encrypt_plaintext(string plaintext, string key); int main(int argc, string argv[]) { int status = check_CLIargs(argc, argv); if (status == 1) { return 1; } string plaintext = get_string("plaintext: "); string ciphertext = encrypt_plaintext(plaintext, argv[1]); printf("ciphertext: %s\n", ciphertext); return 0; } int check_CLIargs(int argc, string argv[]) { if (argc != 2) { printf("Usage: ./substitution key\n"); return 1; } else if (strlen(argv[1]) != 26) { printf("Key must contain 26 characters.\n"); return 1; } for (int i = 0; i < 26; i++) { if (!isalpha(argv[1][i])) { printf("Key must contain 26 alphabetical letters.\n"); return 1; } for (int j = i + 1; j < 26; j++) { if (tolower(argv[1][j]) == tolower(argv[1][i])) { printf("Key must contain 26 distinct letters.\n"); return 1; } } } return 0; } string encrypt_plaintext(string plaintext, string key) { string ciphertext = plaintext; for (int i = 0, n = strlen(plaintext); i < n; i++) { if (islower(plaintext[i])) { ciphertext[i] = tolower(key[plaintext[i] - 97]); } else if (isupper(plaintext[i])) { ciphertext[i] = toupper(key[plaintext[i] - 65]); } } return ciphertext; } ` — Reply to this email directly, view it on GitHub <https://gist.github.com/Latishfaction/b76758b11105e25342c0aac201d6d7e6#gistcomment-4759431> or unsubscribe <https://github.com/notifications/unsubscribe-auth/AHPHDEVJH6QR2OSF53254HTYEJNRHBFKMF2HI4TJMJ2XIZLTSKBKK5TBNR2WLJDHNFZXJJDOMFWWLK3UNBZGKYLEL52HS4DFQKSXMYLMOVS2I5DSOVS2I3TBNVS3W5DIOJSWCZC7OBQXE5DJMNUXAYLOORPWCY3UNF3GS5DZVRZXKYTKMVRXIX3UPFYGLK2HNFZXIQ3PNVWWK3TUUZ2G64DJMNZZDAVEOR4XAZNEM5UXG5FFOZQWY5LFVEYTAMZUG42DMMRUU52HE2LHM5SXFJTDOJSWC5DF> . You are receiving this email because you commented on the thread. Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub> .

Why does it return 1?

Return 1 is another thing for saying that if the input doesn't meet the requirement, it will assume it is false and stop the function and go the next function rather than repeating it, causing errors, and stopping it from going to the next function. Similarly, return 0 is the opposite, it means it will return true, stop the function, and move to the next function.