I understand the necessity of using the modulus operator to compensate for plaintext characters that would surpass Z or z respectively, but I cannot seem to wrap my head around its particular syntax. Could someone briefly explain its usage without providing the exact syntax? See my work in progress below..
#include <stdio.h>
#include <cs50.h>
#include <string.h>
#include <ctype.h>
#include <stdlib.h>
//declare main with command line argument functionality
int main(int argc, string argv[])
{
//return error message if uncorrect # of arguments
if (argc != 2)
{
printf("Please provide one and only one key.\n");
return 1;
}
else
{
//get key from command line arugment
//turn key into integer
int k = atoi(argv[1]);
//prompt for plaintext
printf("plaintext: ");
string p = get_string();
//for each character in plaintext string
for (int i = 0, n = strlen(p); i < n; i++)
{
//create new variable for ith character in plaintext
int a = p[i];
//check if alphabetic and preserve case
if (isalpha(a) && isupper(a))
{
//shift plaintext character by key
int c = (a + k);
//print ciphertext
printf("%c", c);
}
//check if alphabetic and preserve case
else if (isalpha(a) && islower(a))
{
//shift plaintext character by key
int c = (a + k);
//print ciphertext
printf("%c", c);
}
}
printf("\n");
return 0;
}
}
