++i
: is pre-increment the other is post-increment.
i++
: gets the element and then increments it.
++i
: increments i and then returns the element.
Example:
int i = 0;
printf("i: %d\n", i);
printf("i++: %d\n", i++);
printf("++i: %d\n", ++i);
Output:
i: 0
i++: 0
++i: 2