how to convert char to char []

#include <stdio.h>
int main()
{
  char a='a';
  char b[100];


  /*step1: use sprintf func*/
  sprintf(b,"%c",a);
  printf("1: %s \n", b);


  memset(&b, 0x00, sizeof(b));
  
  /*step2: use array set*/
  b[0] = a;
  b[1] = '\0';
  printf("2:  %s\n", b);


  /*use strcpy func*/
  memset(b, 0x00, sizeof(b));
  strcpy(b,&a);
  printf("3:  %s\n",b);
  return 0;
}