Incorrect product of two INT_MAX numbes in C/C++

问题

In my case, product of two INT_MAX numbers is 296447233, which is incorrect.

long long int product = 0;
product = 2137483647 * 2137483647;
printf("product: %lli\n", product);

What I am doing wrong, and how to correct it ?? Thanks !

回答1:

Both of your 2137483647 are of type int. So they stay that type and overflow.

Make them long longs:

product = 2137483647LL * 2137483647LL;

or cast:

product = (long long)2137483647 * 2137483647;

回答2:

Try

product = 2137483647LL * 2137483647LL; 

to ensure that the compile treats the numbers as long long

来源：https://stackoverflow.com/questions/9504477/incorrect-product-of-two-int-max-numbes-in-c-c