Cs50 - Pset 2 - Substitution Program
I was doing the cs50 pset 2 - substitution, where we have to encrypt the plaintext using the key given by the user in the command line, but the following code isn't prompting for an input. What am I doing wrong? Any help would be greatly appreciated!
#include <stdio.h>
#include <cs50.h>
#include <ctype.h>
#include <string.h>
#include <math.h>
int check(int c, string key);
int main(int argc, string argv[])
{
int checkR = check(argc, argv[1]);
if(checkR == 1)
{
return 1;
}
else
{
string key = argv[1];
string ptext = get_string("plaintext: ");
int len = strlen(ptext);
char ctext[len];
for (int i = 0; i < len; i++)
{
if(isupper(ptext[i]))
ctext[i] = toupper(key[(int)ptext[i] - 65]);
else if(islower(ptext[i]))
ctext[i] = tolower(key[(int)ptext[i] - 97]);
else
ctext[i] = ptext[i];
}
printf("ciphertext: %s\n", ctext);
return 0;
}
}
int check(int c, string key)
{
int keyL = strlen(key);
if(c != 2)
return 1;
else if(keyL != 26)
return 1;
for(int i = 0; i < keyL - 1; i++)
{
for(int j = i; j < keyL; j++)
{
if(key[i] == key[j])
return 1;
}
}
return 0;
}
Answer
Answer for the question
In the check
function, you initialized the inner loop as int j = i
.
Therefore, in the first iteration, key[i] == key[j]
will be always true.
Then, 1
is returned from check
and it prevents main
function from printing the prompt.
The initialization should be int j = i + 1
.
Other mistakes
Firstly, it is bad to do int keyL = strlen(key);
before checking c
because key
(argv[1]
) may be NULL
when c
(argc
) is less than 2
.
Secondly, printf("ciphertext: %s\n", ctext);
in this code will invoke undefined behavior because what is stored in ctext
is not NUL-terminated.char ctext[len];
should be char ctext[len+1];
and ctext[len]='\0';
should be added before printf("ciphertext: %s\n", ctext);
.
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