What are the predefined identifiers in c?

This is an identifier that is pre-defined by the system. For example, variables, constants, and functions.

For example, the function we often use, the absolute value function, the system gives abs(x); Find the absolute value of x. In this case, abs is the predefined identifier. So can it be used for other purposes in future programming?

The answer is yes. However, if abs is redefined, it is no longer possible to use it to find absolute values.

So, a predefined identifier is something that has already been defined by the system, but can be redefined by the user.

There is also a relative concept, keywords. This is also defined in advance by the system, but cannot be redefined by the user. For example, if, for, etc.

The undefined identifier workaround is as follows:

Click Items in the menu bar, and then click Properties. You can also right-click the item in the resource window on the right and click Properties.

Then click on C++ and select Optimize.

Then select Disabled (od) in Optimization, OK.

Now go back to debugging, the previous problem of showing undefined identifiers should be solved.

Note: The property configuration of right-clicking in the resource window is only valid for this project, and other projects need to be set again.

What is an undefined variable:

An undefined variable, as the name suggests, is an undefined variable. When programming in the Computer's programmatic language, you accessed undefined or uninitialized variables, resulting in an error in the compiler, and the error message was often there. Not defined" or.

is not defined"or "undeclared".

In computer programming, a variable or scalar is a storage location paired with an associated symbol name (identifier) that contains some known or unknown amount of information called a value. Variable names are the usual way to refer to stored values; This separation of name and content allows the name to be used independently of the exact information it represents.

An identifier in a machine source can be bound to a value at runtime, and the value of a variable may therefore change during program execution.

1.A predefined identifier is one of the three identifiers in the C language and has a specific meaning in the C language. For example, the function "printf" is the full English name plus abbreviation of "format output".

2.Identifiers are divided into keywords, predefined identifiers, and user identifiers.

3.A predefined identifier is a predefined identifier in the C language, such as the name of the system class library, the name of the system constant, and the name of the system function. Predefined identifiers have verbal meanings, such as the function "Format Output" (English full name plus abbreviation:

printf), "format input" (English full name plus abbreviation: scanf), sin, isalnum, etc. Predefined identifiers can be used as user identifiers, but this will lose the intent of the system and cause errors if used incorrectly.

Define an existing symbol with a name of your own.

#define

This is the meaning of macro definition, which is to predefine the meaning of a variable define wm update info (wm user + 1).

Define wm update info as wm user + 1).

Variable names, function names, labels, etc., used in programs are collectively referred to as identifiers.

Except for the name of the library function, which is defined by the system, the rest is defined by the user. c Stipulates that identifiers can only be letters (a z, a z), fissile digits (0 9), and underscores.

A string of characters.

And its first character must be a letter or underscore.

The following must also be noted when using identifiers:

1) Standard C does not limit the length of identifiers, but it is limited by various versions of the C language compilation system, as well as by specific machines. For example, if the first eight bits of an identifier are valid in a certain version c, when the first eight bits of two identifiers are the same, they are considered to be the same identifier.

2) In identifiers, there is a difference between case and case. For example, book and book are two different identifiers.

3) Although identifiers can be defined by programmers at will, identifiers are symbols used to identify a certain quantity. Therefore, the name should be as meaningful as possible to facilitate reading comprehension and "as the name suggests".

Identifier. Variable names, function names, labels, etc., which are used in the program, are collectively referred to as identifiers. Except for the function name of the library function, which is defined by the system, the rest is defined by the user. c

It is stipulated that the identifier can only be a string composed of the letters (a z, a z), the number (0 9), and the underscore ( ), and its first character must be a letter or underscore.