Will `bool` to `int` Conversions Always Behave Predictably in C and C99?

Bool to Int Conversion: Portability and Assertions

In C and even in C99, developers often leverage the implicit conversion from boolean values (bool) to integers (int). However, it is crucial to understand the portability and implications of this conversion to ensure code correctness.

Consider the following code snippets:

int x = 4 < 5;
assert(x == 1);

x = 4 > 5;
assert(x == 0);

What are the expected outputs of these assertions? Are they guaranteed to pass in all contexts?

Portability of Bool to Int Conversion

The implicit conversion from bool to int is defined in the C standard:

• For bool, "false" converts to 0, while "true" converts to 1.
• For C99, where _Bool replaces bool and true/false are macros, the same conversion rules apply.

This conversion is completely portable and guarantees correct behavior across all compliant compilers.

Evaluation of Assertions

Based on the conversion rules, we can evaluate the assertions:

• 4 < 5 evaluates to true, which converts to 1. Thus, x == 1 holds.
• 4 > 5 evaluates to false, which converts to 0. Therefore, x == 0 holds.

Conclusion

Within the context of the provided code, the assertions will pass because the bool to int conversion is implicitly performed and the expected values (1 for "true" and 0 for "false") are assigned correctly. However, it is important to note that this behavior is not limited to the presented code snippets and extends to any situation where such conversions are employed.

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