The following code yields different outputs on different compilers;

#include <stdio.h>

void fun(int x, int y, int z)  /* function definition */
{
    printf("%d %d %d n", x, y, z);  /* 6 6 6 */
}

int main()
{
    int a = 3;
    fun(++a, ++a, ++a);  /* function call */
    return 0;
}

So far the code has yielded the outputs – 6 6 6, 6 5 4, 4 5 6 on different compilers.

Does this behaviour have anything to do with order of evaluation of function arguments or could it be due to calling convention (cdecl)? Will changing to a convention (if that’s possible) change the output of the aforementioned code in any way?

The code snippet is from a book which was trying to introduce calling conventions in C. I’m new to C so please keep it as simple as possible or provide context.