Can C language user identifiers start with numbers?

Can't. The C language stipulates that the identifier cannot start with a number, otherwise the compiler will report an error. This ensures a clear distinction between identifier and numeric literals, avoiding compilation and runtime errors.

Can C language user identifiers start with numbers? The answer is: No! This is not a profound magic, but an iron rule in C grammar. If you try this, the compiler will immediately give you a big warning, or even report an error directly, so that you can know how low-level mistake you have made.

Why is C language so prescribed? There are actually a lot of design philosophy behind this. Think about it, what would happen if the identifier was allowed to start with a number? For example, if you define a variable 1abc , how can the compiler distinguish it from the number 1abc ? This is simply a disaster! When a compiler parses the code, it is necessary to clearly know whether a string is a variable name, a function name, or a pure number. If the identifier can start with a number, the distinction process will become extremely complicated, and may even lead to ambiguity, which will eventually lead to compilation errors or runtime errors. This is like when you remove all the punctuation marks when writing an article, can the article still be understood? The answer is obvious.

Therefore, C language chose a simple, crude, but very effective solution: prohibit the identifier from starting with a number. This allows the compiler to easily identify identifiers and numeric literals, avoiding various potential conflicts and ambiguities. This reflects the pursuit of simplicity and reliability in C language design. It’s like building a house. Only by laying a solid foundation can you build a high-rise building. A robust language specification must start with the most basic grammatical rules and be meticulous.

Of course, there are more than this naming rules for identifiers. You cannot use C language keywords as identifiers, such as int , float , for , etc. These keywords have been pre-occupied by C, and you can no longer use them to name your variables or functions. In addition, it is best to only include letters, numbers and underscores in the identifier, and to be clear and understandable, so that you and others can read and understand it. I've seen too many codes, and variable names are replaced by random letters such as a , b , and c . This kind of code is simply a nightmare and it's crazy to debug.

For another example, suppose you write a program to calculate the area of ​​a circle, and you may define a variable to store the radius of the circle. Instead of using a variable name as simple as r , it is better to use radius , so that the readability of the code will be greatly improved. Good programming habits start with naming. This is not only a matter of personal style, but also a reflection of code quality and maintainability.

Finally, I will share another pit I have stepped on. During a project development, I was negligent and used variable names starting with numbers. As a result, the compiler reported an error, which wasted a lot of time. Since then, I have deeply realized how important it is to abide by the grammatical rules of C. Therefore, remember this rule and develop good programming habits from the beginning to write more elegant and robust C language code. This is not only as simple as avoiding compilation errors, but also the key to improving code quality and reducing bugs.

 <code class="c">#include <stdio.h> // 正确的变量名声明float radius; float area; int main() { radius = 5.0; area = 3.14159 * radius * radius; printf("The area of the circle is: %f\n", area); return 0; } // 错误的变量名声明(编译器会报错) // int 1abc; // 标识符不能以数字开头</stdio.h></code>

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