exam snippet, wont be able to use compiler so can someone explain this?

[xerxes]

#include <stdio.h>

int main()
{
int x=3, i=0;
do{
x=x++;
i++;
}while(i!=3);

printf("%d",x);

return 0;
}

[dev7060]

exam snippet, wont be able to use compiler so can someone explain this?

Explain what?   ⠀⠀