Storing 2^31 in an `int`-CodePudding

Looking at links such as this and this, I understand that unsigned int in C should be of 16 bits. As such, the maximum value that it can store should be 32767.

a. Why can we store INT_MAX in an int variable, such as:

int res=INT_MAX;

b. How is the code like below which calculates the power of 2 valid (runs without any error/warning):

class Solution {
public:
    bool isPowerOfTwo(int n) {
        return n>0 && (!(n&n-1));
    }
};

because the constraints say: -2^31 <= n <= 2^31 - 1, shouldn't we be using long?

CodePudding user response：

a. Why can we store INT_MAX in an int variable, such as:

int res=INT_MAX;

INT_MAX is the maximum value that can be store in int. Per definition that can be stored in an int.

b. How is the code like below which calculates the power of 2 valid (runs without any error/warning): ...

because the constraints say: -2^31 <= n <= 2^31 - 1, shouldn't we be using long?

The constraints are wrong. First they assume int to be 32bit, which is not the case on e.g. AVR. Second they assume int is two's-complement, which is only true since C 20.

It would be more accurate to say the contraints are INT_MIN <= n <= INT_MAX. But really what is the point. The argument is int. That already says that.

Better would be to use unsigned int, uintmax_t or a template. There is no reason to limit this function to int.

Since C 20 there is std::has_single_bit for this.