Identifiers in C

Identifiers in C play an important role in writing organized and meaningful code. They allow programmers to assign readable and manageable names to variables, functions, and other components, making programs easier to understand and maintain.

Here in this blog, we will understand the definition of identifiers in C along with the rules of naming them. We will also read about the importance of using identifiers in programs.

Table of Contents:

• What are Identifiers in C Programming?
  • Why are Identifiers important in C?
• Understanding C Character Set (Foundation)
• Rules for Naming Identifiers in C
• Types of Identifiers in C
• Scope of Identifiers in C
• Difference Between Valid and Invalid Identifiers in C
• Common Errors with Identifiers in C
• Can we use Keywords as Identifiers in C?
• Difference between Keywords and Identifiers
• Naming Conventions and Best Practices
• Best Practices for Identifier Design in Large Codebases
• Difference Between Identifier in C and C++
• Real-Life Examples of C Identifiers
• Conclusion

What are Identifiers in C Programming?

In C programming, identifiers are the names assigned by programmers to the various elements of a program. These include arrays, variables, functions, structures, constants, user-defined types, and labels. These identifiers allow the programmers and the compilers to manipulate data that are stored in memory or to execute specific functionality.

Why are Identifiers important in C?

The identifiers in C are the names that are given to various elements in the program, like functions, arrays, structure variables, and many more, that allow us to refer to and manipulate them through the code. Some of the reasons are given below:

1. Maintainability – When we are modifying the code or updating it, clear identifiers help the developers to understand the structures and purpose of different parts of the code quickly, reducing the effort and time required for maintenance.
2. Readability – To make reading easier, the identifiers in the code are well-named.
3. Reduces Errors and Enhances Debugging – Identifiers reduce confusion, making it easier for programmers to track down bugs, identify incorrect assignments or operations, and understand variable usage.
4. Helps to Differentiate Elements – Identifiers are used by the compiler to differentiate global from local scopes, variables from functions, and types and structures.
5. Reusability – It allows us to define functions in C and reusable blocks of code.

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Understanding C Character Set (Foundation)

The C character set is a set that has a collection of characters that are used and recognized by the C programming language to write programs. These characters form the basic vocabulary from which functions, expressions, statements, and variables are built. Let’s see the C Character Set Used in Identifiers:

1. Alphabets – C language supports both lowercase (a-z) and uppercase (A-Z) English alphabets. For example,
   char group = ‘B’;
   int class;
2. Digits – The C language recognizes the digits (0-9). For example,
   int indexNumber = 30;
3. Special Characters – The C language has a wide range of special characters, used for formatting, syntax structure, and operations. For example,
   int a= 1;
   int b= 3;
   int c= a + b;
   printf(“Intellipaatn”);
4. Use of Whitespace in Identifiers (Unique) – Whitespace, like spaces, tabs, and newlines, is not allowed in the C language within the identifiers, as it is used to separate tokens, not as part of names. For example,
   int roll number = 10;

Naming Rules in C Identifiers

There are various rules for naming an identifier in C. They are as follows:

1. The first character of the identifier can consist of uppercase or lowercase letters or an underscore, but not any digit.
2. The C language is case sensitive, so “Name,” “NAME,” and “name” are three different identifiers.
3. The names of identifiers cannot be C keywords or reserved words, like “int,” “float,” “double,” or “return.”
4. Special characters, like #, $, @, -, *, and ^, are not allowed for naming an identifier.
5. There should not be any tabs, spaces, or other white spaces between the characters of the identifiers.
6. The identifier name can contain digits, letters, and underscores (digits cannot be written as the first character).

Types of Identifiers in C

There are various types of identifiers that are categorized based on their roles. They are as follows:

1. Variable Identifiers – When the names are given to the variables that store the data, then the identifiers are called variable identifiers.
   • For example, char name; here, “name” is a variable identifier.
2. Function Identifiers – The names that are given to the functions in C, blocks of code to perform a specific task, are known as function identifiers.
   • For example, int sum(); where sum is a function identifier.
3. Array Identifiers – The array identifiers are the names given to the arrays, which are the collections of elements of the same data type.
   • For example, int rolls[10]; here, rolls is an array identifier.
4. Constant Identifiers – These are the names given to the constants that remain the same throughout the execution of the program. Often, they are defined using #define or the const keyword.
   • For example, #define gravity 9.8 or int MAX_LENGTH = 50;.
5. Structure and Union Identifiers – When the names are given to the structures or the unions, which are the user-defined data types in C that group together variables of different data types, they are known as structure or union identifiers.
   • For example, struct Employee{….}; or union Students{….};.
6. Typedef Identifiers – The names given to the new data types in C created by using the typedef keyword are known as typedef identifiers.
   • For example,
     typedef unsigned int uint;
     uint roll = 25;
7. Enum Identifiers – These are the names given to the enumerations, which are the user-defined data types that consist of a set of named integer constants.
   • For example, enum Days {Monday, Tuesday, Wednesday, Thursday};.
8. Label Identifier (Goto) – These are the names that are used with the goto statement to mark specific locations in the code and allow the code to jump to that location.
   • For example,
     start:
     printf(“Intellipaatn”);
     goto start.
9. Macro Identifiers (Preprocessor – Unique) – These are the names that are defined using the #define preprocessor directive, which are replaced with their corresponding values during preprocessing.
   • For example, #define MAX_VALUE 50.

Scope of Identifiers in C

The scope of an identifier in the C language refers to the region or part of the program where the identifier, like a function or variable name, can be accessed or used and is valid. It defines where identifiers are visible and usable within the code. There are five types of scope of identifiers in C language. They are as follows:

1. Local Scope – When the identifiers are declared inside a function or block, they are said to have local scope. They are accessible only inside the block.

For example,

void show()
{
    int x = 100; // Here x has the local scope
    printf("%d", x);
}

2. Global Scope – The identifiers that are declared outside the functions are said to have global scope and can be accessed from any function in the same file.

For example,

int a = 50; //it is declared outside the function, making it a global variable
void display(){
    printf("%d", a); //it is accessible inside the function
}

3. Block Scope – In block scope, the identifiers are declared within the brackets “{ }” (i.e., inside conditions, loops, etc.) and are limited to that particular block only. It is a subset of local scope in C.

For example,

int main(){
if (5){
int num = 30; // Here, block scope has been used, which is accessed within this block.
printf(“%d”, num);
}
}

4. Function Scope (Label Scope) – The function scope in C is used by labels that are used in goto, meaning they can only be referenced inside the same function in which they are declared.

For example,

void scope() {
    start: // label has function scope
    printf("Intellipaatn");
    goto start;
}

Static Identifiers and Lifetime

A static identifier refers to a function or variable that is declared with the static keyword. It provides specific characteristics related to its memory allocation, deallocation, and visibility.

Lifetime of a Static Identifier

The lifetime of a static identifier spans the entire execution duration of the program, which means

1. Initialization – The static variables are initialized at the beginning of the program’s execution, only once. If they are not explicitly initialized, static variables are implicitly initialized to zero (for arithmetic types), NULL (for pointers), or equivalent defaults.
2. Persistence – The values of the static variables remain the same throughout the program’s execution. Their memory is allocated in the data segment of the program’s memory.
3. Deallocation – Deallocation of the static variables occurs only when the program is terminated.

Difference Between Valid and Invalid Identifiers in C

Given below is the difference between valid and invalid identifiers in C:

Common Errors with Identifiers in C

There are some common errors with identifiers in C; they are as follows:

1. The pre-defined keywords (like int, double, float) cannot be used as identifiers, as these are the reserved words in C.
2. The C language is a case-sensitive language, which means “NAME,” “name,” and “Name” will be treated as three different identifiers.
3. Identifiers can only contain alphabets, digits, and underscores, but not special characters.
4. Identifiers must have an uppercase or lowercase alphabet or underscore at the beginning, but not a digit.
5. Due to scopes, using identifiers outside of the block of code can sometimes create an error.
6. If the same identifier is used more than once in the same scope or the name of the identifier is too long, then it will throw a compilation warning.
7. If an identifier is declared but not defined in the function or the variables in C across multiple files, then it throws a linker error.

Can Keywords Be Used as Identifiers in C?

If we are using keywords in C as identifiers (for example, if we are naming a variable “int” even though “int” is a keyword), it will result in compilation errors. Keywords are reserved words, which means they have a particular meaning in the programming language and cannot be used for other purposes, like naming variables or functions. If we are trying to utilize a keyword other than its reserved purpose, the compiler will regard the code as invalid and will not translate the code to executable code.

Difference between Keywords and Identifiers

In C programming, keywords are predefined reserved words, while identifiers are user-defined names, making the difference between keywords and identifiers crucial for writing valid, error-free code.

Naming Conventions and Best Practices

The way of naming the variables, functions, and other identifiers in C programming has a vital effect on code readability, usage, and collaboration with the developers. By understanding established naming practices, we can establish clarity, reduce confusion, and reduce the potential for errors, and it will be easier for us and other programmers to understand the code when we encounter it again down the road.

The best practice is to use meaningful and descriptive names. When we are naming identifiers, avoid using generic names like x, temp, and val for names that describe the purpose of the variable. Other than using these examples, use examples like totalMarks, studentName, or calculateAverage.

All the above examples make more sense, are more intuitive, and are much easier to follow over time than the mentioned examples. There can be an instances where shorter names could be used when we have scoped the names tightly (for example, a common practice in loop variables the int for- or while-loop variables would be limited to i; or j; ) Name some identification, but as a rule, if you can’t see enough of the code to remember what average is referencing in the rest of your code, then you need to name it a little more explicitly. Anything wrapping more than a couple of lines, you should be using more descriptive names than cryptic names.

Best Practices for Identifier Design in Large Codebases

Naming is simple in small programs, but in large projects where many people write thousands of lines of code, naming gets difficult.

1. Namespace Simulation in C

Unlike C++, the C language does not support namespaces. Thus, you can run into name collision (two or more different files using the same name for a function or variable) issues.

Solution: Use prefixes to stimulate namespaces

Example:

// In math_utils.c
int math_add(int a, int b);

// In string_utils.c
int string_add(char* s1, char* s2);

2. Using Prefixing to Avoid Name Collisions

The basic concept of prefixing is easy. Simply add a small tag before your function or variable name, letting you know which module it resides in.

Example:

int ui_draw_button(); // "ui_" tells it's part of the user interface code
int db_connect(); // "db_" shows it's from the database module

Tips for Modular Code

• Group related functions into one file.
• Use header files to declare public functions.
• Prefix all identifiers with the module name.
• Avoid global variables unless there is no alternative.
• Adhere to naming conventions agreed upon by your team.

Identifiers in C vs C++

Given below is the difference between an identifier in C and C++

Real-Life Examples of C Identifiers

1. In System Programs

There are many common identifiers used in system-level code, such as the C standard library:

• Main: The entry point of every C program.
• Printf: Used for printing output.
• Scanf: Used for reading input.

Example:

int main() {
    printf("Hello, world!");
    return 0;
}

2. In User-Defined Programs

In user-defined programs, users create their identifiers according to their needs.

Example:

int student_age;
float calculate_average(float marks[]);
void display_report();

C Identifier Examples with Code:

Some examples of using identifiers in different ways are given below:

1: Variable and Function Identifiers

In this code, we are using variable and function identifiers. Identifiers are used to give names to these variables and the functions. The variables are used to store the data, and the functions are the block of code that performs a specific task.

Output

2: Structure Identifiers

In this C program, we will see how a structure identifier is used. The name of the structure identifier used is “Student.” The structure is a user-defined data type that groups different data types under a single name.

Output

3: Typedef Identifier

In this program, we will see the use of typedef identifiers. The typedef is a keyword that is used to create a new name for an existing data type.

Output

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Conclusion

In C programming, identifiers in C can be used to name variables, functions, arrays, structures, and constants. By correctly using identifiers in C, using sensible names, and avoiding invalid identifiers, you can increase the readability, debug ability, and maintainability. Knowing how identifiers work in C (local, global, block, and static) and whether or not they are required to follow certain naming conventions and best practices, helps to create error-free and polished code. C programming does not use namespaces, so naming identifiers with prefixes, for example, helps handle conflicts in large projects. Knowing how to declare and use identifiers in C programming is an executed step towards delivering clean, efficient, and scalable code.

Identifiers in C – FAQs