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Keywords, Identifiers & Variables in C

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Introduction

When you start learning programming, you will often come across terms like keywords, identifiers, and variables. These are the basic building blocks of any C program.

Understanding these concepts clearly will help you write programs correctly and avoid common mistakes.

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What are Keywords in C?

Keywords are reserved words in C that have a predefined meaning.
You cannot use them as names for variables or functions.

👉 They are part of the C language itself.

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Examples of Keywords

• int
• float
• if
• else
• return
• while

👉 These words are already defined by the compiler.

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⚠️ Important Rule

❌ You cannot use keywords as variable names

Example:

int int = 10; // ❌ Invalid

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What are Identifiers?

Identifiers are the names given to variables, functions, arrays, etc.

👉 They help us identify different elements in a program.

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Examples of Identifiers

int age;
float salary;
int totalMarks;

Here:

• age, salary, totalMarks → identifiers

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Rules for Identifiers

• ✔ Must start with a letter or underscore _
• ✔ Can contain letters, digits, underscore
• ✔ Cannot start with a number
• ✔ Cannot be a keyword
• ✔ Case-sensitive (age ≠ Age)

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What are Variables?

A variable is a named memory location used to store data.

👉 It allows us to store and manipulate values in a program.

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Syntax of Variable Declaration

data_type variable_name;

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Examples

int age = 20;
float price = 99.5;
char grade = 'A';

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Example Program

#include <stdio.h>

int main() {
    int age = 18;
    float height = 5.9;
    char grade = 'A';

    printf("Age = %d\n", age);
    printf("Height = %f\n", height);
    printf("Grade = %c\n", grade);

    return 0;
}

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Output

Age = 18
Height = 5.900000
Grade = A

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Explanation of the Program

• int, float, char → Keywords (data types)
• age, height, grade → Identifiers
• Values assigned → Variables storing data

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Difference Between Keywords, Identifiers & Variables

Feature	Keywords	Identifiers	Variables
Meaning	Reserved words	Names of elements	Storage locations
Defined by	Language	Programmer	Programmer
Example	int, if	age, total	int age = 20;

Common Mistakes

• ❌ Using keywords as identifiers
• ❌ Starting identifier with number
• ❌ Forgetting data type
• ❌ Case mismatch

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Pro Tips

• ✔ Use meaningful variable names (totalMarks instead of t)
• ✔ Follow naming conventions
• ✔ Keep names simple and clear
• ✔ Practice writing small programs

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Conclusion

Keywords, identifiers, and variables are the foundation of C programming. Once you understand these clearly, writing programs becomes much easier and more structured.

👉 This article is part of Dharani Tech Edu Hub — where learning programming is made simple and practical.