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


int main (void)
{
  char * test="This is a secret message"; // test input
  const int SHIFT=9; // the shift
  char * coded = malloc(strlen(test)+1); // get memory of same size
  for (int i=0; i<strlen(test); i++) // go through input
    *(coded+i)=*(test+i) + SHIFT; // write to output, + SHIFT
  *(coded+strlen(test))=0; // make sure have 0 at the end
  printf("Coded: %s\n",coded); // display it
// Result: Coded: ]qr|)r|)j)|nl{n})vn||jpn

  return 0;
}