Why the output is 22?Help with abstraction

Question

#include <stdio.h>
#include <stdlib.h>

int main()
{
int a=0;
printf("%d%d\n",++a,++a);

return 0;

}

Answer 1

this called undefined behaviour
u modify the same variable more than once in one expressions
we dont know how it behave or in what order it is evaluated
there are other ways to achieve the same thing but this one is not recommended

Answer 2

So what are the other ways