************c macro Stringizing operator (#)
This operator causes the corresponding actual argument to be
enclosed in double quotation marks.
//对应的对应参数为到双引号括起来
#include <stdio.h>
#define mkstr(s) #s
int main(void)
{
printf(mkstr(geeksforgeeks));
return 0;
}

***Token-pasting operator (##)
Allows tokens used as actual arguments to be concatenated to form other tokens
作为真正参数的标记可以连接为其他标记
This is called token pasting or token concatenation. The ‘##’ pre-processing operator performs token pasting.
//执行标记粘贴
When a macro is expanded, the two tokens on either side of each ‘##’ operator are combined into a single token,
//展开宏时，##两边的token合成为一个
which then replaces the ‘##’ and the two original tokens in the macro expansion
#include <stdio.h>
#define concat(a, b) a##b
int main(void)
{
int xy = 30;
printf("%d", concat(x, y));
return 0;
}