Constants and Variables in C

A variable is a named object whose stored value can change while a program runs. A constant represents a value that should not be modified by the program after it is defined.

Variables in C Top ↑

int count = 10;
double price = 45.75;
char grade = 'A';

The variable name identifies the value so it can be read or changed later.

Variable Naming Rules Top ↑

• Use letters, digits and underscores.
• The first character cannot be a digit.
• Spaces and punctuation such as - are not allowed inside an identifier.
• C keywords such as int, return and while cannot be used as variable names.
• C is case-sensitive, so total and Total are different identifiers.

my_var
page1
student_count

Integer, Floating and Character Constants Top ↑

Constants written directly in source code are often called literals.

345        // integer constant
-543       // integer constant
125.34     // floating constant
3.2e2      // exponential floating constant
'B'        // character constant
"Welcome"  // string literal

Read-Only Objects with const Top ↑

#include <stdio.h>

int main(void) {
    const int max_users = 45;
    const char grade = 'A';
    const char message[] = "Welcome";

    printf("Maximum users: %d\n", max_users);
    printf("Grade: %c\n", grade);
    printf("Message: %s\n", message);
    return 0;
}

Output

Maximum users: 45
Grade: A
Message: Welcome

The const qualifier tells the compiler that your program should not modify that object through its declared name.

Variables Can Change Top ↑

int score = 45;
printf("%d\n", score);

score = 50;
printf("%d\n", score);

Output

45
50

Next, learn how the location of a declaration affects visibility and lifetime in local, global and static variables.

Subhendu Mohapatra

Author & Instructor at plus2net

I write and maintain practical tutorials on Python, PHP, SQL, JavaScript, HTML, jQuery, and web development at plus2net. The tutorials focus on clear explanations, working examples, and code that readers can test and adapt while learning.

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