编译出错，什么意思？
double float a;
printf("a=%df\n",10/3);

[解决办法]
楼主是想要有效数字或宽度吧?

参考这样就行:

C/C++ code

 printf("%.*f", 3, 10.0 / 3); printf("%*d", 3, 10 / 3);