Caesar Cipher.c-HackerRank

Problem-Julius Caesar protected his confidential information by encrypting it using a cipher. Caesar's Cipher shifts each letter by a number of letters. If the shift takes you past the end of the alphabet, just rotate back to the front of the alphabet. In the case of a rotation by 3, w, x, y and z would map to z, a, b and c.

Original alphabet:      abcdefghijklmnopqrstuvwxyz
Alphabet rotated +3:    defghijklmnopqrstuvwxyzabc

For example, the given cleartext  and the alphabet is rotated by . The encrypted string is .

Note: The cipher only encrypts letters; symbols, such as -, remain unencrypted.

Solution-

#include <assert.h>

#include <limits.h>

#include <math.h>

#include <stdbool.h>

#include <stddef.h>

#include <stdint.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

int main(){

    int n; 

    scanf("%d",&n);

    char* s = (char *)malloc(10240 * sizeof(char));

    scanf("%s",s);

    int k,x; 

    scanf("%d",&k);

    for(int i=0; i<=strlen(s);i++){

        if( isalpha(s[i]) ){

            if( isupper(s[i]) )

             x='A';

            else

               x='a';

           int a=(int)s[i];

               a= x+((a+k-x)%26);

           char c=a;

               s[i]=c;

        }        

    }

    printf("%s",s);

    return 0;

}

Link to the problem:-

https://www.hackerrank.com/challenges/caesar-cipher-1/problem