void increment(int x)
{
    x = x + 1;
}

int main(void)
{
    int i = 1, j = 2;
    increment(i); /* now i becomes 2 */
    increment(j); /* now j becomes 3 */
    return 0;
}

i和j变为2和3吗，大家讨论下！！十分简单！！