What is the priority of C language !x?

The logical non-operator (!) has the priority after brackets, which means that in expressions, it will precede most other operators. Understanding priority not only requires rote memorization, but more importantly, understanding the logic and potential pitfalls behind it to avoid undetectable errors in complex expressions. Adding brackets can clarify expression intent, improve code clarity and maintainability, and prevent unexpected behavior.

Priority of C language !x : A silly thoughts of an old bird

You ask me the priority of !x ? This question seems simple, but it actually has a hidden mystery. Many beginners, even some people who claim to be veterans, may fall apart here. Simply put, ! is a logical non-operator, which has a high priority, second only to parentheses () . This means that in expressions, ! will be executed precedence over most other operators.

Don't be fooled by this simple answer! There is a story behind this. Many times, we understand priority, not just the priority table of rote operators, but more importantly, we understand the logic and potential pitfalls behind it.

Think about it, if you wrote !xy , do you think you should add xy first and then reverse it? wrong! The compiler will calculate !x first, and then add. Why? Because ! high. This seemingly inconspicuous little detail can easily lead to undetectable bugs in complex expressions.

Let me give you another example, !x || y && z . This thing looks a lot of trouble, but if you understand the priority, it will be much simpler. The compiler will calculate !x first, then y && z , and finally || . Remember that logic is not ! has priority over logic or || and logic with && . If you are not sure, the best way is to add brackets to make your intentions clear at a glance. (!x) || (y && z) , writing this way will make the code clear and not prone to errors, and it will also facilitate others to understand your code. This is the old bird's experience!

Let's use code to verify it, and by the way, take a look at some less common pitfalls:

 <code class="c">#include <stdio.h> #include <stdbool.h> int main() { int x = 5; int y = 2; int z = 0; bool result1 = !xy; // 先计算!x (0), 然后0 y (2) bool result2 = !x || y && z; // 先!x (0), 然后y && z (0), 最后0 || 0 (0) bool result3 = (!x) || (y && z); // 加括号，更清晰printf("result1: %d\n", result1); // 输出2 printf("result2: %d\n", result2); // 输出0 printf("result3: %d\n", result3); // 输出0 // 更复杂的情况，为了防止意外，加括号是王道int a = 10; int b = 5; int c = 2; int d = (!ab) * c; //这里可能会有问题，不加括号会让人难以理解int e = ((!(ab)) b) * c; // 加括号后，代码逻辑清晰，不容易出错printf("d = %d\n", d); printf("e = %d\n", e); return 0; }</stdbool.h></stdio.h></code>

See? In the code, I have explained the calculation process of each expression with comments. This is exactly the attitude you should have when writing code: clear, concise, and easy to understand . Priority is just a tool, and the ultimate goal is to write high-quality code to make the program run stably and make the code easy to maintain. Don't sacrifice code readability and maintainability in pursuit of so-called "skills". Remember, the code is written for people to see, and the second is executed for machines.

So, remember the priority of ! and more importantly, understand its role in expressions and how to avoid potential errors. Write more code and think more, and you will naturally become a true programming expert. Don’t forget that the old bird also comes from the rookie.

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