C++ Data Types, Variables, and I/O

1. Primitive Data Types

Fundamental Types:

cpp

// Integer Types (whole numbers)
int age = 25;               // Typically 4 bytes (-2.1B to 2.1B)
short smallNumber = 100;    // 2 bytes (-32,768 to 32,767)
long bigNumber = 100000L;   // 4 or 8 bytes
long long hugeNumber = 1000000000LL; // 8 bytes

// Floating-Point Types (decimal numbers)
float price = 19.99f;       // 4 bytes (6-7 decimal digits precision)
double pi = 3.1415926535;   // 8 bytes (15 decimal digits precision)
long double precise = 3.141592653589793238L; // 10-16 bytes

// Character Types
char grade = 'A';           // 1 byte (-128 to 127)
wchar_t wideChar = L'Ω';    // 2 or 4 bytes (wide character)
char16_t utf16Char = u'字'; // 2 bytes (UTF-16)
char32_t utf32Char = U'😀'; // 4 bytes (UTF-32)

// Boolean Type
bool isReady = true;        // 1 byte (true or false)
bool isDone = false;

// Void Type
void noReturn();            // No value (used for functions)

Type Ranges and Memory Usage:

2. sizeof Operator

cpp

#include <iostream>
using namespace std;

int main() {
    cout << "Size of data types:" << endl;
    cout << "bool: " << sizeof(bool) << " byte" << endl;
    cout << "char: " << sizeof(char) << " byte" << endl;
    cout << "short: " << sizeof(short) << " bytes" << endl;
    cout << "int: " << sizeof(int) << " bytes" << endl;
    cout << "long: " << sizeof(long) << " bytes" << endl;
    cout << "float: " << sizeof(float) << " bytes" << endl;
    cout << "double: " << sizeof(double) << " bytes" << endl;
    
    // Using sizeof with variables
    int num = 100;
    double value = 3.14;
    cout << "\nSize of variables:" << endl;
    cout << "num (int): " << sizeof(num) << " bytes" << endl;
    cout << "value (double): " << sizeof(value) << " bytes" << endl;
    
    // Size of expressions
    cout << "\nSize of expressions:" << endl;
    cout << "5 + 3: " << sizeof(5 + 3) << " bytes" << endl;
    cout << "3.14 * 2: " << sizeof(3.14 * 2) << " bytes" << endl;
    
    return 0;
}

Output varies by system/compiler:

text

Size of data types:
bool: 1 byte
char: 1 byte
short: 2 bytes
int: 4 bytes
long: 8 bytes
float: 4 bytes
double: 8 bytes

3. Type Modifiers

cpp

#include <iostream>
using namespace std;

int main() {
    // SIGNED (default - can be positive or negative)
    signed int s1 = -100;      // Same as int
    signed char sc = -128;
    
    // UNSIGNED (only positive values, larger positive range)
    unsigned int ui = 4294967295U;  // Max value for 4-byte unsigned
    unsigned short us = 65535;      // 0 to 65,535
    unsigned char uc = 255;         // 0 to 255
    
    // SIGNED vs UNSIGNED comparison
    signed int si = -10;
    unsigned int ui2 = 10;
    
    cout << "Signed int: " << si << endl;
    cout << "Unsigned int: " << ui2 << endl;
    cout << "Max unsigned int: " << ui << endl;
    
    // Mixing signed and unsigned (caution!)
    signed int x = -5;
    unsigned int y = 10;
    cout << "\nMixing signed/unsigned (dangerous):" << endl;
    cout << "x + y = " << x + y << endl;  // Unexpected result!
    
    return 0;
}

4. Constants (const, constexpr)

cpp

#include <iostream>
using namespace std;

int main() {
    // CONST - value cannot be changed after initialization
    const double PI = 3.14159;
    const int MAX_STUDENTS = 100;
    const string COMPANY_NAME = "MyCorp";
    
    // PI = 3.14;  // Error: assignment of read-only variable
    
    cout << "PI: " << PI << endl;
    cout << "Max Students: " << MAX_STUDENTS << endl;
    
    // const with pointers
    int value = 10;
    const int* ptr1 = &value;      // Pointer to constant int
    int* const ptr2 = &value;      // Constant pointer to int
    const int* const ptr3 = &value; // Constant pointer to constant int
    
    // *ptr1 = 20;  // Error: cannot modify through ptr1
    // ptr2 = nullptr; // Error: cannot change ptr2 itself
    
    // CONSTEXPR - evaluated at compile time (C++11+)
    constexpr double SPEED_OF_LIGHT = 299792458.0;
    constexpr int ARRAY_SIZE = 100;
    constexpr int SQUARE_OF_5 = 5 * 5;
    
    // constexpr functions (C++11+)
    constexpr int square(int x) {
        return x * x;
    }
    
    constexpr int squaredValue = square(10);  // Computed at compile time
    
    cout << "Speed of light: " << SPEED_OF_LIGHT << endl;
    cout << "Square of 10: " << squaredValue << endl;
    
    // const vs constexpr
    int input;
    cout << "Enter a number: ";
    cin >> input;
    
    const int runtimeConst = input;     // OK - initialized at runtime
    // constexpr int compileTimeConst = input;  // Error - needs compile-time value
    
    return 0;
}

5. Input & Output (cin, cout)

cpp

#include <iostream>
#include <string>
using namespace std;

int main() {
    // Basic Output
    cout << "Hello, World!" << endl;  // endl adds newline
    cout << "Welcome to C++" << '\n'; // '\n' also adds newline
    
    // Basic Input
    int age;
    string name;
    
    cout << "\nEnter your name: ";
    cin >> name;                       // Reads single word
    
    cout << "Enter your age: ";
    cin >> age;
    
    cout << "Hello " << name << ", you are " << age << " years old." << endl;
    
    // Multiple inputs
    int x, y, z;
    cout << "\nEnter three numbers: ";
    cin >> x >> y >> z;
    cout << "Sum: " << (x + y + z) << endl;
    
    // Reading strings with spaces
    string fullName;
    cout << "\nEnter your full name: ";
    cin.ignore();                      // Clear newline from previous input
    getline(cin, fullName);           // Reads entire line with spaces
    
    cout << "Full name: " << fullName << endl;
    
    // Character input
    char initial;
    cout << "\nEnter your initial: ";
    cin >> initial;
    cout << "Initial: " << initial << endl;
    
    // Mixed input types
    int id;
    double salary;
    char department;
    
    cout << "\nEnter ID, salary, and department: ";
    cin >> id >> salary >> department;
    cout << "Employee #" << id << " earns $" << salary 
         << " in department " << department << endl;
    
    return 0;
}

6. Formatting Output

cpp

#include <iostream>
#include <iomanip>  // For formatting
using namespace std;

int main() {
    // Setting precision for floating-point
    double pi = 3.141592653589793;
    
    cout << "Default: " << pi << endl;
    cout << "Fixed (2 decimal): " << fixed << setprecision(2) << pi << endl;
    cout << "Scientific: " << scientific << pi << endl;
    
    // Setting width and alignment
    cout << "\nText Formatting:" << endl;
    cout << setw(15) << left << "Name" 
         << setw(10) << right << "Score" << endl;
    cout << setw(15) << left << "Alice" 
         << setw(10) << right << 95.5 << endl;
    cout << setw(15) << left << "Bob" 
         << setw(10) << right << 87.25 << endl;
    
    // Integer formatting
    int num = 255;
    cout << "\nInteger formatting:" << endl;
    cout << "Decimal: " << dec << num << endl;
    cout << "Hexadecimal: " << hex << num << endl;
    cout << "Octal: " << oct << num << endl;
    
    // Reset to decimal
    cout << dec;
    
    // Fill character
    cout << "\nFill character:" << endl;
    cout << setfill('*') << setw(20) << "Hello" << endl;
    
    // Boolean formatting
    bool flag = true;
    cout << "\nBoolean formatting:" << endl;
    cout << "Default: " << flag << endl;
    cout << boolalpha << "As text: " << flag << endl;
    
    // Show positive sign
    cout << "\nShowing positive sign:" << endl;
    cout << showpos << 42 << " " << -42 << endl;
    cout << noshowpos;  // Turn off
    
    return 0;
}

7. Escape Sequences

cpp

#include <iostream>
using namespace std;

int main() {
    // Common Escape Sequences
    cout << "Escape Sequences Examples:\n" << endl;
    
    // Newline
    cout << "Line 1\nLine 2\nLine 3" << endl;
    
    // Tab
    cout << "\nTabbed Output:" << endl;
    cout << "Name:\tAlice" << endl;
    cout << "Age:\t25" << endl;
    cout << "City:\tNew York" << endl;
    
    // Backspace
    cout << "\nBackspace: ABC\b\bD" << endl;  // Prints "AD" (ABC then backspace twice)
    
    // Carriage return
    cout << "Loading: 0%\rLoading: 50%\rLoading: 100%" << endl;
    
    // Backslash and quotes
    cout << "\nPath: C:\\Users\\Name\\Documents" << endl;
    cout << "Quote: She said, \"Hello!\"" << endl;
    cout << "Single quote: It\'s raining" << endl;
    
    // Alert (beep)
    cout << "\aAlert! (You might hear a beep)" << endl;
    
    // Vertical tab and form feed
    cout << "Vertical\vTab\vExample" << endl;
    
    // Unicode/Octal/Hexadecimal characters
    cout << "\nSpecial characters:" << endl;
    cout << "Euro symbol: \u20AC" << endl;      // Unicode
    cout << "Copyright: \xA9" << endl;          // Hexadecimal
    cout << "Smiley: \1" << endl;               // Octal (may not work on all systems)
    
    // Raw string literals (C++11) - no escape sequences processed
    cout << "\nRaw string literal:" << endl;
    cout << R"(Path: C:\Users\Name\Documents\nNo newline here)" << endl;
    
    // Multi-line string
    cout << "\nMulti-line output:" << endl;
    cout << "Line 1\n"
         << "Line 2\n"
         << "Line 3" << endl;
         
    return 0;
}

8. Complete Example Combining Everything

cpp

#include <iostream>
#include <iomanip>
#include <string>
using namespace std;

constexpr double TAX_RATE = 0.07;
const int MAX_ITEMS = 10;

int main() {
    // Variable declarations with different types
    string itemName;
    int quantity;
    double price, subtotal, tax, total;
    
    // Input with formatting
    cout << "=== SHOPPING CART ===\n" << endl;
    cout << "Enter item name: ";
    getline(cin, itemName);
    
    cout << "Enter quantity: ";
    cin >> quantity;
    
    cout << "Enter price per item: $";
    cin >> price;
    
    // Calculations
    subtotal = quantity * price;
    tax = subtotal * TAX_RATE;
    total = subtotal + tax;
    
    // Formatted output
    cout << fixed << setprecision(2);
    cout << "\n" << string(30, '=') << endl;
    cout << "RECEIPT" << endl;
    cout << string(30, '-') << endl;
    cout << left << setw(15) << "Item:" << itemName << endl;
    cout << left << setw(15) << "Quantity:" << quantity << endl;
    cout << left << setw(15) << "Unit Price:" << "$" << price << endl;
    cout << left << setw(15) << "Subtotal:" << "$" << subtotal << endl;
    cout << left << setw(15) << "Tax (" << TAX_RATE * 100 << "%):" << "$" << tax << endl;
    cout << left << setw(15) << "Total:" << "$" << total << endl;
    cout << string(30, '=') << endl;
    
    // Using sizeof
    cout << "\nMemory usage:" << endl;
    cout << "int: " << sizeof(int) << " bytes" << endl;
    cout << "double: " << sizeof(double) << " bytes" << endl;
    cout << "string: " << sizeof(string) << " bytes" << endl;
    
    return 0;
}