Variables

Introduction

Variables are named regions of memory with a fixed type. C requires a declaration before first use so the compiler knows how much space to reserve.

Understanding the topic

Declaration Specify type and name: int count;

Initialization Assign at declaration: int count = 10; or later: count = 10;

Naming rules Letters, digits, underscore; cannot start with a digit; case-sensitive.

• Declaration — Specify type and name: int count;.
• Initialization — Assign at declaration: int count = 10; or later: count = 10;.
• Naming rules — Letters, digits, underscore; cannot start with a digit; case-sensitive.

Step-by-step explanation

1. Declaration — Specify type and name: int count;.
2. Initialization — Assign at declaration: int count = 10; or later: count = 10;.
3. Naming rules — Letters, digits, underscore; cannot start with a digit; case-sensitive.

Syntax reference

Syntax reference:

type variableName;
type variableName = value;

Informative example

Example program:

#include <stdio.h>

int main(void) {
    int years = 30;
    float rate = 2.5f;
    char band = 'B';
    printf("%d %.1f %c\n", years, rate, band);
    return 0;
}

30 2.5 B

Execution workflow

Best practices

• Enable warnings: gcc -Wall -Wextra -std=c11 source.c -o app
• Give every variable a defined value before it is read.
• Stay inside array bounds — C will not stop you from over-running a buffer.

Common mistakes

• Reading uninitialized storage — behavior is undefined.
• Dismissing compiler warnings instead of fixing root causes.
• Ignoring NULL returns from malloc, fopen, and similar APIs.

Hands-on exercise

Practice problems:

• Declare variables of different types
• Print values with correct format specifiers

Summary

Variables in C — Typed, named storage — declare before use.