Integer times integer overflow

Let's look at an example , Put two 32 Bit Int Type number multiplication , Assign the result to long Type variable .
long a=111111 * 111111;
At first glance, there seems to be nothing wrong with it , But this is a pit , Jump carefully ！ The value after multiplication will overflow .

reason ：
For compilers ,int and int Multiply , The result also exists first int in , With be assigned to long still longlong Fields of data type have no relationship .

terms of settlement ：
Want not to overflow , Just put two 32 Bits are forced to long type , Multiply again .