Bool Conversion to Int: Guaranteed to Be 0 or 1?

In programming languages like C and C, bool is commonly used to represent boolean values of true and false. However, behind the scenes, these values are often stored as integers. This raises the question: when a bool is converted to an int, is the result guaranteed to be either 0 or 1?

C

In C , the answer is a resounding yes. According to the C standard (§4.5/4), "An rvalue of type bool can be converted to an rvalue of type int, with false becoming zero and true becoming one." This means that when a bool is converted to an int in C , the result will always be 0 or 1.

C

In C, the situation is slightly different but equally clear. According to the C standard (§6.3.1.2/1), "When any scalar value is converted to _Bool, the result is 0 if the value compares equal to 0; otherwise, the result is 1." This implies that when a bool (represented as _Bool in C) is converted to an int, the result will again be 0 or 1.

Practical Example

To illustrate this behavior in code:

int a = 2;
bool b = a;
int c = 3   b; // 4

In this example, the bool variable b is initialized to the value of int a (which is 2), but since bool values are stored as 0 or 1, b becomes 1. The subsequent addition of 3 results in c being assigned the value 4. This confirms that bool is converted to int as 1, guaranteeing a result of 0 or 1.