PSET 2 Caesar: Permission denied problem

Question

I'm having trouble running my code because of a permission denial...Could someone please help me? THanks :)

Here's my code:

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

int main(int argc, string argv[])
{
    if (argc == 2 && isdigit(*argv[2]))
    {
        printf("Usage: ./caesar key\n");
        return 1;
        
    }
    int cle = atoi(argv[1]);
    
    string m = get_string("Please enter plaintext here: ");
    
    printf("Here is the ciphertext translation: ");
   
    for (int i = 0, p = strlen(m) ; i < p; i++)
    {
         if (m[i] <= 'Z' && m[1] >= 'A')
        {
            
        printf("%c", (((m[1] - 'A') + cle) % 26) + 'A');
        }
        
        else if (m[1] <= 'z' && m[1] >= 'a')
        
        { 
          printf("%c", (((m[1] - 'a') + cle) % 26) + 'a');
    }
    
    else 
    
    {
        
    printf("%c", m[1]);
    
    }
    
printf("\n");
 return 0;
    }
    
 
    
    {
        printf ("Usage: ./caesar k\n");
        return 1;
    }


}

Answer 1

A segmentation fault is not a permission error. It's a memory access error. The code is trying to access memory it shouldn't.

Specifically, the error lies here: isdigit(*argv[2])

The isdigit() function takes a single character as input. argv[2] is a string (or char array). When you give a string as a parameter to isdigit or any of it's cousin functions, it will generate a seg fault.

The code needs to check each char in the argv[2] string. I suggest you try a for loop.

Tip: Check out the following: Do YOU know how to find a seg fault?? Advice to new programmers

Answer 2

You're trying to run the uncompiled .c code instead of the binary.

Try running:

./caesar