Understanding Constants, Variable Declarations, and Statements in C

 

Constants, Variables & Statements in C

The Essential Building Blocks of C Programming

In C programming, everything revolves around data and how we use it. To work with data, we use constants, variables, and statements. These are the building blocks of every program.

Let's explore these concepts in a simple and clear way.

What is a Constant in C?

A constant is a value that never changes during program execution. Think of it like your date of birth—it remains fixed forever!

Why Use Constants?

• Keep values fixed

• Improve code readability

• Avoid accidental changes

Types of Constants

1. Integer Constants

10, -25, 1000

2. Floating-point

3.14, -0.01

3. Character

'A', '%'

4. String

"Hello", "C Language"

Declaring Constants in C

1. Using #define

#define PI 3.14

Compiler replaces PI with 3.14 everywhere

2. Using const

const int speedLimit = 60;

Cannot be changed after declaration

What is a Variable?

A variable is a named memory location where you can store and change data during program execution.

Why Use Variables?

• Store user input

• Perform calculations

• Make programs dynamic

Naming Rules

• Start with letter or _

• No spaces/special chars

• Avoid keywords

• Examples: age, total_marks

Declaring Variables in C

Declaration Only

int age;
float price;
char grade;

With Initialization

int age = 20;
float price = 99.5;

What are Statements in C?

A statement is an instruction that tells the program what to do. Think of them as sentences in a story.

Types of Statements

1. Declaration

int x;

2. Assignment

x = 10;

3. I/O

scanf("%d", &x);

printf("%d", x);

4. Control

if, else, while, for

Constant vs Variable

Feature	Constant	Variable
Value	Never changes	Can change
Declaration	#define or const	With data type
When fixed	Compile time	Can change at runtime

Code Example

#include <stdio.h>
#define PI 3.14

int main() {
    const int daysInWeek = 7;
    int radius = 5;
    float area;

    area = PI * radius * radius;

    printf("Area: %.2f\n", area);
    return 0;
}

Elements used:

• Constants: PI, daysInWeek

• Variables: radius, area

• Statements: declaration, assignment, printf

Importance of Proper Declarations

• Saves memory

• Makes code readable

• Avoids errors

• Creates efficient programs

Common Mistakes to Avoid

• Changing constant values

• Using undeclared variables

• Misspelling variable names

• Forgetting semicolons

Summary

• Constants: Fixed values that never change

• Variables: Storage that holds changing values

• Statements: Commands that make programs work

Master these elements to build powerful C programs!

FAQs

Q1. Can I use same name for constant and variable?

No, it can confuse the compiler and readers.

Q2. What happens if I change a constant?

The compiler will give an error.

Q3. Why do statements end with semicolons?

It tells the compiler the instruction is complete.

Q4. Can I declare multiple variables at once?

Yes: int a, b, c;

Q5. Must variables be declared before use?

Yes, in C every variable must be declared first.