first program

/**
 * ============================================================
 * YOUR FIRST C++ PROGRAM
 * ============================================================
 * 
 * This file walks you through the anatomy of a C++ program.
 * 
 * To compile and run:
 *   g++ -std=c++17 03_first_program.cpp -o first_program
 *   ./first_program
 * 
 * ============================================================
 */

// ============================================================
// PART 1: PREPROCESSOR DIRECTIVES
// ============================================================

/*
 * Lines starting with # are preprocessor directives.
 * They are processed BEFORE compilation.
 * 
 * #include tells the preprocessor to insert the contents
 * of another file at this location.
 */

#include <iostream>  // Input/Output stream library
                     // Provides: cout, cin, endl, etc.

#include <string>    // String library
                     // Provides: std::string class

// ============================================================
// PART 2: THE MAIN FUNCTION
// ============================================================

/*
 * Every C++ program MUST have exactly one main() function.
 * This is where program execution begins.
 * 
 * int main() means:
 *   - 'int' = the function returns an integer
 *   - 'main' = the function name (special - entry point)
 *   - '()' = no parameters (you can also use int argc, char* argv[])
 */

int main() {
    // ========================================================
    // PART 3: STATEMENTS
    // ========================================================
    
    /*
     * Statements are instructions that perform actions.
     * Each statement ends with a semicolon (;)
     * 
     * std::cout = "standard character output" (console output)
     * << = insertion operator (sends data to output)
     * std::endl = end line (newline + flush buffer)
     */
    
    // Simple output
    std::cout << "Hello, World!" << std::endl;
    
    // Multiple items in one statement
    std::cout << "Welcome to " << "C++ Programming!" << std::endl;
    
    // Using variables
    std::string name = "Learner";
    int year = 2024;
    
    std::cout << "Hello, " << name << "!" << std::endl;
    std::cout << "You're learning C++ in " << year << std::endl;
    
    // ========================================================
    // PART 4: COMMENTS
    // ========================================================
    
    // This is a single-line comment
    
    /* 
     * This is a 
     * multi-line comment
     */
    
    // Comments are ignored by the compiler
    // Use them to explain your code!
    
    // ========================================================
    // PART 5: RETURN STATEMENT
    // ========================================================
    
    /*
     * The return statement ends the function and sends
     * a value back to the caller.
     * 
     * For main():
     *   return 0; = Program executed successfully
     *   return non-zero; = Program had an error
     * 
     * The operating system receives this value.
     */
    
    return 0;  // Success!
}

// ============================================================
// PROGRAM OUTPUT:
// ============================================================
/*
Hello, World!
Welcome to C++ Programming!
Hello, Learner!
You're learning C++ in 2024
*/

// ============================================================
// KEY TAKEAWAYS:
// ============================================================
/*
 * 1. #include brings in external code
 * 2. Every program needs main()
 * 3. Statements end with semicolons
 * 4. std::cout outputs to console
 * 5. << chains multiple outputs
 * 6. return 0 indicates success
 */

// ============================================================
// EXERCISES:
// ============================================================
/*
 * 1. Modify the program to print your own name
 * 2. Add more cout statements with different messages
 * 3. Try removing a semicolon - see what error you get
 * 4. Try removing #include <iostream> - see what happens
 * 5. Change return 0 to return 1 - check echo $? after running
 */