C Variables

A variable in C is a named place in memory where a program can store a value. You choose the variable name, choose what kind of value it can hold, and then use that name later in the program.

Declaring Variables

Before you use a variable in C, you must declare it. A declaration tells the compiler the variable’s type and name.

int age;

This creates a variable named age that can store an integer value. The type int means whole numbers such as 5, 42, or -3.

Assigning Values

After declaring a variable, you can store a value in it with the assignment operator =. You can also declare and assign in one statement.

#include <stdio.h>

int main(void)
{
    int age = 21;

    printf("Age: %d\n", age);
    return 0;
}

Output:

Age: 21

In the printf call, %d is a placeholder for an int value. The variable age is passed after the string, so its stored value is printed in that position.

Changing A Variable

A variable can be assigned a new value after it already has one. The old value is replaced.

#include <stdio.h>

int main(void)
{
    int score = 10;
    printf("First score: %d\n", score);

    score = 15;
    printf("Updated score: %d\n", score);

    return 0;
}

Output:

First score: 10
Updated score: 15

Notice that the second assignment uses score = 15;, not int score = 15;. The variable was already declared, so you only write its name when giving it a new value.

Using More Than One Variable

Programs often use several variables at the same time. Each variable should have a name that describes what it stores.

#include <stdio.h>

int main(void)
{
    int apples = 6;
    int oranges = 4;
    int total = apples + oranges;

    printf("Apples: %d\n", apples);
    printf("Oranges: %d\n", oranges);
    printf("Total fruit: %d\n", total);

    return 0;
}

Output:

Apples: 6
Oranges: 4
Total fruit: 10

The variable total stores the result of adding apples and oranges. When a variable appears in an expression, C uses the value currently stored in that variable.

Variable Names

C variable names must follow a few rules:

• They can contain letters, digits, and underscores.
• They must not start with a digit.
• They must not be a C keyword such as int or return.
• They are case-sensitive, so score and Score are different names.

Choose names like student_count, price, or total_score instead of vague names like x when the meaning matters.

Common Beginner Mistakes

• Declare a variable before using it.
• Use one = for assignment.
• Do not redeclare the same variable in the same block.
• Use the correct printf placeholder for the type you are printing.

The key idea is that variables let a C program remember values and reuse them. Next, you will learn more about C data types and the different kinds of values variables can store.