What is happening to the printf function? - c

Question

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?

Answer 1

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];

Answer 2

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.