🔤 Unit 2: Data Types, Variables & Constants

Welcome back, coder-in-training! 👋
In this unit, we’ll dive into the building blocks of C — data types, variables, and constants.
Think of these as the alphabet of programming: once you master them, you can form meaningful “sentences” (programs). ✨

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📦 Data Types in C

Data types tell the computer what kind of data you want to store.

🏗 Primary Data Types

Data Type	Keyword	Size (bytes)	Range	Format Specifier
Character	char	1	-128 to 127	%c
Integer	int	4	-2,147,483,648 to 2,147,483,647	%d or %i
Float	float	4	3.4E-38 to 3.4E+38	%f
Double	double	8	1.7E-308 to 1.7E+308	%lf
Void	void	0	No value	-

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🛠 Data Type Modifiers

Modifiers tweak the size and range of basic data types:

Modifier	Used With	Purpose
short	int	Reduces size (2 bytes)
long	int, double	Increases size
signed	int, char	Allows negatives (default)
unsigned	int, char	Only positive values

short int a;           // 2 bytes: -32,768 to 32,767
long int b;            // 8 bytes: larger range
unsigned int c;        // 0 to 4,294,967,295
unsigned char d;       // 0 to 255
long long int e;       // Very large numbers

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🏷 Variables

A variable is like a box 📦 with a label — you can store a value and change it later.

Declaration Syntax

datatype variable_name;

// Examples
int age;
float salary;
char grade;

Initialization Styles

Step-by-step

int age;
age = 25;

Direct

int age = 25;

Multiple

int x, y, z;
int a = 10, b = 20, c = 30;

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Naming Rules ✅❌

✅ Must start with a letter or underscore
✅ Case sensitive (age, Age, AGE are different)
❌ No spaces, no special symbols, no keywords

// Good
int studentAge;
float total_salary;
char GRADE;
int _privateVar;

// Bad
int a;
int x1234;
int myVariableForStoringTheAgeOfStudent;

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🗿 Constants

Constants are values that cannot change once set. Like your date of birth 🎂.

Types of Constants

🔢 Literals

10, -50, 0x1A, 077   // Integers
3.14, -0.5, 2.5e3    // Floating
'A', '5', '\n'       // Characters
"Hello"              // Strings

🔖 Symbolic Constants

#define

#define PI 3.14159
#define MAX_SIZE 100
#define NEWLINE '\n'

const keyword

const int DAYS_IN_WEEK = 7;
const float GRAVITY = 9.81;
const char GRADE = 'A';

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🎹 Escape Sequences

Sequence	Meaning
\n	New line
\t	Tab
\\	Backslash
\"	Double quote
\'	Single quote
\0	Null terminator
\b	Backspace
\r	Carriage return

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➕ Operators

Operators are the tools 🔧 that let you work with values.

Arithmetic Operators

Operator	Example	Meaning
+	a + b	Add
-	a - b	Subtract
*	a * b	Multiply
/	a / b	Divide
%	a % b	Remainder

Integer Division

int result1 = 10 / 3; // Result = 3

Float Division

float result2 = 10.0 / 3; // Result = 3.333...

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Relational Operators

Operator	Example	Meaning
==	a == b	Equal
!=	a != b	Not equal
>	a > b	Greater
<	a < b	Less
>=	a >= b	Greater/Equal
<=	a <= b	Less/Equal

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Logical Operators

| Operator | Example | True If... | | -------- | --------------------- | --------------- | -------- | --- | --------- | ----------------- | | && | (a > 5) && (b < 10) | Both true | | | | | (a > 5) | | (b < 10) | At least one true | | ! | !(a > 5) | Reverses result |

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Assignment Operators

Operator	Example	Equivalent
=	a = 5	Assign
+=	a += 3	a = a + 3
-=	a -= 3	a = a - 3
*=	a *= 3	a = a * 3
/=	a /= 3	a = a / 3
%=	a %= 3	a = a % 3

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Increment & Decrement

Pre-increment

int a = 5, b;
b = ++a;  // a = 6, b = 6

Post-increment

int a = 5, b;
b = a++;  // b = 5, then a = 6

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Conditional (Ternary)

status = (age >= 18) ? "Adult" : "Minor";
int max = (a > b) ? a : b;

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🔄 Type Conversion

Implicit

int a = 10;
float b = 5.5;
float result = a + b; // a converted to float

Explicit (Casting)

int a = 10, b = 3;
float result = (float)a / b; // 3.333...

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🎓 Complete Example

#include <stdio.h>
#define PI 3.14159

int main() {
    const int MAX_MARKS = 100;
    int marks = 85;
    float percentage;
    char grade;

    percentage = (float)marks / MAX_MARKS * 100;

    grade = (percentage >= 90) ? 'A' :
            (percentage >= 80) ? 'B' :
            (percentage >= 70) ? 'C' :
            (percentage >= 60) ? 'D' : 'F';

    printf("=== Student Report Card ===\n");
    printf("Marks: %d/%d\n", marks, MAX_MARKS);
    printf("Percentage: %.2f%%\n", percentage);
    printf("Grade: %c\n", grade);

    if (marks >= 40 && marks <= MAX_MARKS) {
        printf("Status: PASS\n");
    } else {
        printf("Status: FAIL\n");
    }

    int bonus = 5;
    marks += bonus;
    printf("After bonus: %d\n", marks);

    return 0;
}

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📝 Quick Quiz

What is the difference between pre-increment and post-increment?

• No difference
• Pre-increment increases before using, post-increment after ✅