how to encrypt and decrypt a zip file

void encrypt(void)
{
  char c;
  int key = 5;
 
  printf("Enter a message to encrypt: ");
 
  while((c = getchar()) != '\n')
     putchar(c + key);
}
 
void decrypt(void)
{
  char c;
  int key = 5;
 
  printf("Enter a message to decrypt: ");
 
  while((c = getchar()) != '\n')
     putchar(c - key);
}