For prefix increment:
printf( "%d" , ++a);
The output will be 11. I am sure you understand it why?
For postfix increment:
printf( "%d" , a++);
The output will be 10. It is because, the value of a is returned first then only it is increased by 1.
Here is another example:
int a=10, b;
printf( "%d" , a++); // 10 is displayed
++a; // a becomes 12 after this statement
In you example, it doesn't matter if you use prefix or postfix increment but there are cases when, prefix and postfix increment gives different result.