Copy and Concatenation strcpy strcat

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

int main(void)
{
  /* Always ensure that your string is large enough to contain the characters
   * and a terminating NUL character ('\0')!
   */
  char mystring[10];

  /* Copy "foo" into `mystring`, until a NUL character is encountered. */
  strcpy(mystring, "foo");
  printf("%s\n", mystring);

  /* At this point, we used 4 chars of `mystring`, the 3 characters of "foo",
   * and the NUL terminating byte.
   */

  /* Append "bar" to `mystring`. */
  strcat(mystring, "bar");
  printf("%s\n", mystring);

  /* We now use 7 characters of `mystring`: "foo" requires 3, "bar" requires 3
   * and there is a terminating NUL character ('\0') at the end.
   */

  /* Copy "bar" into `mystring`, overwriting the former contents. */
  strcpy(mystring, "bar");
  printf("%s\n", mystring);

  return 0;
}

foo
foobar
bar