C command line argument validation errors - c

Question

Thank you everyone who helped me yesterday. I have one more issue with my code.
The purpose of the program is to take a command line argument and use it as a key to encrypt some plaintext entered by the user and to shift it by the number of letters given. The program should accept a single command-line argument, a non-negative integer. If any of the characters of the command-line argument is not a decimal digit, the program should print the message Usage: ./caesar key and return from main a value of 1.
When I test it, I receive the following error messages:
handles lack of key
failed to execute program due to segmentation fault
:( handles non-numeric key
timed out while waiting for program to exit
#include <cs50.h>
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
//Declare the encrypting function
void encrypt(string plaintext, int k, string ciphertext);
int main(int argc, string argv[])
{
string plaintext;
int n = strlen(plaintext);
char ciphertext[n+1]; //the lenght of the plaintext+ 1 extra char which i
int k = atoi(argv[1]); //Convert string into an integer, i.e parsing
if (argc != 2)
{
printf("Usage: ./caesar key\n");
return 1;
}
else
{
for (int i = 0, m = strlen(argv[1]); i < m; i++)
{
if (isdigit(argv[1][i]))
{
plaintext = get_string("Plaintext:");
encrypt(plaintext, k, ciphertext); //calling the encryption function
printf("ciphertext: %s\n", ciphertext);
return 0;
}
else
{
printf("Usage: ./caesar key\n");
return 1;
}
}
}
}
void encrypt(string plaintext, int k, string ciphertext)
{
for (int i = 0, n = strlen(plaintext); i < n; i++)
{
if (isupper(plaintext[i]))
{
int pi = plaintext[i] - 65;
char ci = ((pi + k) % 26) + 65;
ciphertext[i] = ci;
}
else if (islower(plaintext[i]))
{
int pi1 = plaintext[i] - 97;
char ci1 = ((pi1 + k) % 26) + 97;
ciphertext[i] = ci1;
}
else
{
ciphertext[i] = plaintext[i];
}
}
}

Answer 1

I've updated your code as little as possible. Most of it was just re-arranging things.
int main(int argc, string argv [])
{
// Check for correct number of args
if (argc != 2)
{
puts("Please supply a key.");
puts("Usage: ./caesar key");
return 0;
}
// Check that argv[1] is all digits (i.e. positive integer)
for (int i = 0, n = strlen(argv[1]); i < n; i++) {
if (!isdigit(argv[1][i])) {
puts("Usage: ./caesar key");
return 1;
}
}
// Get user string
string plaintext = get_string("Plaintext:");
if (!plaintext) return 1;
// My compiler does not allow VLAs so I use malloc
char *ciphertext = malloc(strlen(plaintext) + 1);
int k = atoi(argv[1]); //Convert string into an integer, i.e parsing
encrypt(plaintext, k, ciphertext); //calling the encryption function
printf("ciphertext: %s\n", ciphertext);
// Free up allocated mem
free(ciphertext);
free(plaintext);
return 0;
}
void encrypt(string plaintext, int k, string ciphertext)
{
int n = strlen(plaintext);
for (int i = 0; i < n; i++)
{
if (isupper(plaintext[i]))
{
int pi = plaintext[i] - 65;
char ci = ((pi + k) % 26) + 65;
ciphertext[i] = ci;
}
else if (islower(plaintext[i]))
{
int pi1 = plaintext[i] - 97;
char ci1 = ((pi1 + k) % 26) + 97;
ciphertext[i] = ci1;
}
else
{
ciphertext[i] = plaintext[i];
}
}
// Don't forget to append nul-terminator
ciphertext[n] = '\0';
}