C语言字符串内存问题

#include <stdio.h>

int main(void){
    char * a = {"hello"};
    char * b = {'h','f','\0'};
    char * c = {'h','f'};
    char * e = {'h','f',' '};
    printf("%d\n",strlen(a));
     //printf("%d",strlen(b)); //内存出错
     // printf("%d",strlen(c)); //内存出错
      //printf("%s\n",b);   //出错
      //printf("%d\n",strlen(e)); //出错

    char d[10] ={'a','b'};
    for(int i =0;i<10 ;++i){
        printf("%c\n",d[i]);
    }
    printf("%d\n",strlen(d));
    return 0;

}

待定