CPP Data Types and Variables – CS201 VU

C++ Data Types and Variables – CS201 VU Guide

Understanding data types and variables is the foundation of learning any programming language, including C++. If you're a CS201 student at Virtual University (VU), this guide will break down the topic in simple terms, enriched with examples, memory insights, and best practices to help you master the basics.

🔹 What Are Variables in C++?

A variable is a named storage that holds data. Think of it like a labeled box that stores values.

int age = 21;
float weight = 65.5;
char grade = 'A';

🔹 Why Are Data Types Important?

• Tell the compiler how much memory to allocate
• Specify what kind of data can be stored
• Define what operations are allowed

🔹 Categories of Data Types in C++

1. Basic (Primitive) Data Types
2. Derived Data Types
3. Enumeration Data Types
4. User-defined Data Types

1. Basic Data Types

Data Type	Description	Size	Example
int	Integer	4 bytes	int marks = 90;
float	Decimal (single precision)	4 bytes	float pi = 3.14;
double	Decimal (double precision)	8 bytes	double g = 9.8;
char	Character	1 byte	char grade = 'A';
bool	Boolean	1 byte	bool isPassed = true;

2. Derived Data Types

• Arrays: int numbers[5];
• Pointers: int *ptr = #
• Functions: int sum(int a, int b);
• References: int& ref = x;

3. Enumeration (enum) Data Types

enum Day { SUNDAY, MONDAY, TUESDAY };
Day today = MONDAY;

4. User-defined Data Types

struct Student {
  int id;
  char name[50];
};

🔹 Declaring and Initializing Variables

int age;
int score = 95;
int x = 5, y = 10, z = 15;

Naming Rules

• Must start with a letter or underscore
• Case-sensitive
• No spaces or special characters
• Cannot be a reserved keyword

🔹 Constants in C++

const float PI = 3.14159;

🔹 Memory Allocation and Size

cout << sizeof(int); // Outputs 4

Signed vs Unsigned

unsigned int u = 4294967295;

🔹 Type Conversion (Casting)

Implicit Conversion

int x = 5;
float y = x;

Explicit Conversion

float x = 3.14;
int y = (int)x;

🔹 Variable Scope

• Local: Inside functions
• Global: Outside all functions
• Static: Retains value between calls

void demo() {
  static int counter = 0;
  counter++;
  cout << counter;
}

🔹 Best Practices

• Use meaningful names
• Initialize variables
• Use const for constants
• Use the correct data type
• Comment your variables

🔹 Common Mistakes

Mistake	Description
Uninitialized variables	Contain garbage values
Wrong type operations	e.g., adding int to string
Overflows	Exceeding max range of data type
Typos	Wrong variable names

🔹 Sample Program

#include <iostream>
using namespace std;

int main() {
  const float PI = 3.14159;
  int radius = 5;
  float area = PI * radius * radius;

  cout << "Radius: " << radius << endl;
  cout << "Area: " << area << endl;

  return 0;
}

🔹 FAQ

• Q: Which type for age?
  A: Use int.
• Q: Can I store numbers in char?
  A: Yes, but they represent ASCII codes.
• Q: Is double better than float?
  A: More precise, but takes more memory.
• Q: Are global variables bad?
  A: Not always, but they can lead to poor structure.

🔹 Conclusion

Mastering data types and variables in C++ is crucial for CS201 and your programming journey. This guide covered primitive types, constants, memory allocation, scope, and common practices to help you write clean, reliable code.

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