Identifiers in C

Introduction to Identifiers in C

In C programming, identifiers are names given to various program elements like variables, functions, arrays, etc. Identifiers make it easier for programmers to understand the code, as they allow referencing different parts of the program by meaningful names.

Rules for Identifiers

Character Set: Identifiers can contain alphabets (both uppercase and lowercase), digits, and underscores (_).
Case-Sensitive: Identifiers in C are case-sensitive (example and Example are considered different identifiers).
Cannot Start with a Digit: Identifiers must start with an alphabet or an underscore, not a digit.
Keywords Not Allowed: C keywords (like int, float, if, etc.) cannot be used as identifiers.
No Special Characters: Identifiers cannot include special characters other than an underscore (_).

As per the above rules, some examples of the valid and invalid identifiers are:

Valid C Identifiers:

age, Age, AGE, average_age, __temp, address1, phone_no_personal, _my_name

Invalid C Identifiers:

Average-age, my name, $age, #phone, 1mg, phy+maths

Syntax for writing Identifiers

<data_type> identifier_name;

Example of Identifiers using C program

#include <stdio.h>

// Function prototype
void greetUser();

// Global variable
int count = 5;

int main() {
    // Local variable
    int localValue = 10;

    greetUser(); // Function call

    printf("Global count: %d\n", count);        // Print global variable
    printf("Local value: %d\n", localValue);    // Print local variable

    return 0;
}

// Function definition
void greetUser() {
    printf("Hello, user!\n");
}

Explanation

#include <stdio.h>: Includes the standard input-output library to use functions like printf.
int count = 5;: A global variable named count initialized with a value of 5, accessible throughout the program.
int localValue = 10;: A local variable named localValue initialized with a value of 10, accessible only within the main function.
greetUser();: Calls the greetUser function to print a greeting message.
printf("Global count: %d\n", count): Prints the value of the global variable count to the console.
printf("Local value: %d\n", localValue): Prints the value of the local variable localValue to the console.
void greetUser(): Defines the greetUser function, which prints a greeting message to the console.

Types of Identifiers in C

Variable Identifiers: Names given to variables, such as age, height, etc.
Function Identifiers: Names assigned to functions, such as printData, calculateSum, etc.
Array Identifiers: Names given to arrays, like data, values, etc.

Example of Variable Identifier

int marks1 = 50, marks2 = 60;
float avg = (float) (marks1 + marks2) / 2;

Example of Function Identifier

int average(int marks1, int marks2) 
{
    return (float) (marks1 + marks2) / 2;
}

Example of User-define Identifier

struct student 
{
    int rollno;
    char *name;
    int m1, m2, m3;
    float percent;
};

struct student s1 = {1, "Raju", 50, 60, 70, 60.00};

Common Mistakes with Identifiers

Using Keywords: Attempting to name an identifier with a reserved keyword, like int, float.
Starting with a Digit: Naming an identifier like 2data instead of data2.
Special Characters: Using characters like #, @, & which are not allowed in identifiers.

Best practice for writing identifiers

Meaningful Names: Use descriptive names that indicate the purpose of the identifier, like totalAmount or calculateAverage.
Consistent Casing: Follow a consistent casing style (e.g., camelCase for variables, PascalCase for function names).
Avoid Long Names: Keep identifiers concise but meaningful, avoiding overly long names.

Conclusion

Identifiers are fundamental in making the code readable, organized, and understandable for others working on the same code. Remember to follow the rules and best practices for creating effective identifiers in C programs.