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]));
            }
        }
    }
}

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.