What is happening to the printf function?-CodePudding

I am attempting to write the substitution program here https://cs50.harvard.edu/x/2022/psets/2/substitution/

here is my code:

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

int main(int argc, string argv[1])
{
    if (argc > 2 || argc < 2){
        printf("Plz 1 word in command \n");
        return 1;
    }
    int sum = 0;
    string arg1 = argv[1];


    //test
    for (int i = 0; i < strlen(arg1); i  ){
        if (isalpha(arg1[i]) == 0){
            printf("plz only alphabet character \n");
            return 1;
        }}
    // convert all key to upper
    for (int i = 0; i < strlen(arg1); i  ){
        arg1[i] = toupper(arg1[i]);
     }
    for (int i = 0; i < strlen(arg1); i  ){
          sum = sum   (int)(arg1[i]);
    }
    if (strlen(arg1) != 26){
        printf("Plz input 26 char \n");
        return 1;
    } else if (sum != 2015){printf("no oveerlapping letter plz \n");
    return 1; }
    //test finish
    string al = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    string pt = get_string("plaintext: ");
    char pt1[strlen(pt)]; 
    char cp[strlen(pt)]; 
    // all plain text to upper
    for (int i = 0; i < strlen(pt); i  ){
        pt1[i]=toupper(pt[i]);
    }
    //scan
    for (int a = 0; a < strlen(pt); a  ){
        char b = pt1[a];
        for (int i = 0; i < strlen(al); i  ){
             if ( al[i] == b){
                   cp[a] = arg1[i];
                   break;
             } else {
                cp[a] = b;
             }
        }
    //case preserve
      if (islower(pt[a])){
         cp[a] = tolower(cp[a]);
    }} 

       printf("ciphertext: %s \n", cp);
       return 0;
}

when i type in the key YTNSHKVEFXRBAUQZCLWDMIPGJO and then type "hello!1 lmao" as plaintext, here is what i receive

substitution/ $ ./substitution YTNSHKVEFXRBAUQZCLWDMIPGJO
plaintext: hello!1 lmao
ciphertext: ehbbq!1 bayq�

it should only show ehbbq!1 bayq but it is showing more letter than i intended, there might be other letter or simbol after "bayq", can someone explain to me what is going on and why there are additional text in my output?

CodePudding user response：

You need a null terminatig character (usually it is character having integer value 0) to terminate the string

    size_t a;
    for (a = 0; a < strlen(pt); a  )
    {
        char b = pt1[a];
        for (int i = 0; i < strlen(al); i  )
        {
             if ( al[i] == b)
             {
                   cp[a] = arg1[i];
                   break;
             } else {
                cp[a] = b;
             }
        }
    //case preserve
        if (islower((unsigned char)pt[a]))
        {
            cp[a] = tolower((unsigned char)cp[a]);
        }
    }
    cp[a]  = 0;

you need to pass unsigned char to functions like tolower. I did not analyze the logic of your code as it is your home work.

Also cp is too short, it has to be char cp[strlen(pt) 1];

CodePudding user response：

Your char arrays as declared are too short to handle copies of the data, due to the need for a null-terminator att the end.

    char pt1[strlen(pt)]; 
    char cp[strlen(pt)];

Rather you need to do:

    char pt1[strlen(pt)   1]; 
    char cp[strlen(pt)   1];

However, the other approach would be to simply use strdup to dynamically allocate sufficient storage and copy the data.

    char pt1 = strdup(pt); 
    char cp = strdup(pt);

Of course, any function that returns dynamically allocated memory (likely including cs50's get_string) means you should remember to free that memory. And ensure it actually succeeded.