C++ Basics
C++ is a powerful, general-purpose programming language created as an extension of the C language. It adds object-oriented features to C, allowing for both procedural and object-oriented programming approaches.
Key Concepts and Definitions
1. Your First C++ Program
Program: A set of instructions that tells the computer what to do.
#include: A preprocessor directive that tells the compiler to include a specific file
iostream: A header file that contains functions for input/output operations.
main(): The entry point of a C++ program. Execution always begins here.
std::cout: The standard output stream used to display output.
std::endl: Inserts a newline character and flushes the output buffer.
#include <iostream>
int main() {
std::cout << "Hello, World!" << std::endl;
return 0;
}
Program Structure Diagram:
┌─────────────────────────────────────────────┐
│ #include <iostream> │ ← Preprocessor directive
│ │
│ int main() { │ ← Main function (entry point)
│ std::cout <<"Hello, World!"<<std::endl; │ ← Output statement
│ return 0; │ ← Return statement
│ } │
└─────────────────────────────────────────────┘
Output:
Hello, World!
2. Variables and Data Types
Variable: A named storage location in memory that holds a value of a specific type.
Data Type: Defines the kind of data a variable can store and how much memory it occupies.
Data Types Table:
┌───────────────────────────────────────────────────────┐
│ C++ Basic Data Types │
├───────────────┬───────────────────┬───────────────────┤
│ Type │ Example │ Memory (typical) │
├───────────────┼───────────────────┼───────────────────┤
│ int │ 25, -10, 0 │ 4 bytes │
│ float │ 19.99f, -3.5f │ 4 bytes │
│ double │ 3.14159265359 │ 8 bytes │
│ char │ 'A', '7', '$' │ 1 byte │
│ bool │ true, false │ 1 byte │
│ std::string │ "John", "Hello" │ Variable │
└───────────────┴───────────────────┴───────────────────┘
#include <iostream>
int main() {
// Integer types
int age = 25; // Whole number
// Floating-point types
float price = 19.99f; // Decimal number (single precision)
double precise_value = 3.14159265359; // Decimal number (double precision)
// Character type
char grade = 'A'; // Single character
// Boolean type
bool is_active = true; // true or false
// String (from standard library)
std::string name = "John"; // Text
// Output
std::cout << "Age: " << age << std::endl;
std::cout << "Price: $" << price << std::endl;
std::cout << "Grade: " << grade << std::endl;
std::cout << "Active: " << is_active << std::endl;
std::cout << "Name: " << name << std::endl;
return 0;
}
Output:
Age: 25
Price: $19.99
Grade: A
Active: 1
Name: John
3. Input and Output
Input: Data provided to the program, typically from the user.
Output: Data produced by the program, typically displayed to the user.
#include <iostream>
#include <string>
int main() {
std::string name;
int age;
// Output
std::cout << "Enter your name: ";
// Input
std::getline(std::cin, name);
std::cout << "Enter your age: ";
std::cin >> age;
// Output with variables
std::cout << "Hello, " << name << "! You are " << age << " years old." << std::endl;
return 0;
}
Input and Output Diagram:
┌──────────────┐ ┌──────────────────┐ ┌──────────────┐
│ │ │ │ │ │
│ User │────▶│ C++ Program │────▶│ Console │
│ │ │ │ │ │
└──────────────┘ └──────────────────┘ └──────────────┘
│ ▲ │
│ │ │
│ │ │
└──────────────────────┴───────────────────────┘
Data flow (input/output)
Example Interaction:
Enter your name: Alice
Enter your age: 30
Hello, Alice! You are 30 years old.
4. Operators
Operator: A symbol that tells the compiler to perform specific mathematical or logical operations.
Operators Table:
┌─────────────────────────────────────────────────────────┐
│ C++ Operators │
├────────────────┬────────────────────┬───────────────────┤
│ Category │ Operators │ Example │
├────────────────┼────────────────────┼───────────────────┤
│ Arithmetic │ +, -, *, /, % │ a + b = 13 │
│ Comparison │ ==, !=, >,<, >=, <=│ a > b = true │
│ Logical │ &&, ||, ! │ x && y = false │
│ Assignment │ =, +=, -=, *=, /= │ a += 2 (a = a + 2)│
│ Increment │ ++, -- │ a++ (a = a + 1) │
└────────────────┴────────────────────┴───────────────────┘
#include <iostream>
int main() {
// Arithmetic operators
int a = 10, b = 3;
std::cout << "a + b = " << (a + b) << std::endl; // Addition
std::cout << "a - b = " << (a - b) << std::endl; // Subtraction
std::cout << "a * b = " << (a * b) << std::endl; // Multiplication
std::cout << "a / b = " << (a / b) << std::endl; // Division (integer)
std::cout << "a % b = " << (a % b) << std::endl; // Modulus (remainder)
// Comparison operators
std::cout << "a == b: " << (a == b) << std::endl; // Equal to
std::cout << "a != b: " << (a != b) << std::endl; // Not equal to
std::cout << "a > b: " << (a > b) << std::endl; // Greater than
std::cout << "a < b: " << (a < b) << std::endl; // Less than
// Logical operators
bool x = true, y = false;
std::cout << "x && y: " << (x && y) << std::endl; // Logical AND
std::cout << "x || y: " << (x || y) << std::endl; // Logical OR
std::cout << "!x: " << (!x) << std::endl; // Logical NOT
return 0;
}
*Output:
a + b = 13
a - b = 7
a * b = 30
a / b = 3
a % b = 1
a == b: 0
a != b: 1
a > b: 1
a < b: 0
x && y: 0
x || y: 1
!x: 0
Arrays
Array: A collection of elements of the same type stored in contiguous memory locations.
#include <iostream>
int main() {
// Declare and initialize an array
int numbers[5] = {10, 20, 30, 40, 50};
// Access array elements
std::cout << "First element: " << numbers[0] << std::endl;
std::cout << "Third element: " << numbers[2] << std::endl;
// Modify an element
numbers[1] = 25;
std::cout << "Modified second element: " << numbers[1] << std::endl;
// Loop through array
std::cout << "All elements: ";
for (int i = 0; i < 5; i++) {
std::cout << numbers[i] << " ";
}
std::cout << std::endl;
return 0;
}