C Language Study - the use of symbol '##'

##

#include <stdio.h>

#define INTVARIABLE(n) i##n

int main(void)

{

int INTVARIABLE(2) = 3;

printf("i2=%d\n",i2);//output i2=3

i2 = 5;

printf("i2=%d\n",i2);//output i2=5

return 0;

}