Second week

Week 2: Basic Syntax and Structure

• Writing your first program
• Understanding the main function
• Basic input and output (cin, cout)
• Comments

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Writing Your First Program

Let's start by writing our first C++ program. This simple program prints 'Hello, World!' to the console. The essential structure includes #include <iostream>, which includes the input-output stream library. The int main() { ... } function defines the main function where the execution of the program begins. Inside the main function, std::cout is used for outputting text to the console, and return 0; indicates that the program has completed successfully."

• Start with the essential structure:

  #include <iostream>

  int main() {
      std::cout << "Hello, World!" << std::endl;
      return 0;
  }

• #include <iostream>: Includes the input-output stream library.
• int main() { ... }: Defines the main function where execution starts.
• std::cout: Standard character output stream.
• return 0;: Indicates successful completion.

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Understanding the Main Function

Now, let's delve deeper into the main function. The int main() { ... } is the entry point of every C++ program and it returns an integer value to the operating system. The return 0; statement indicates that the program ended successfully. Non-zero values typically indicate an error or special exit status. There are other possible main function signatures, like int main(int argc, char* argv[]), which are used for handling command-line arguments."

• int main() { ... }
  • Entry point of every C++ program.
  • Returns an integer value to the operating system.
• return 0;
  • Indicates that the program ended successfully.
  • Non-zero values typically indicate an error or special exit status.
• Other possible main function signatures:
  • int main(int argc, char* argv[])
  • Used for command-line arguments.

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Basic Input and Output (cin, cout)

Next, let's look at basic input and output using cin and cout. std::cout is used for outputting text to the console. For example, std::cout << "Enter a number: "; prompts the user to enter a number. std::cin is used for inputting data from the user. For example, int num; std::cin >> num; reads an integer entered by the user. Here's a complete example that combines both cin and cout to prompt the user for a number and then display it back to them.

• std::cout: Used for output.
  • Example:

  std::cout << "Enter a number: ";
  

• std::cin: Used for input.
  • Example:

    int num;
    std::cin >> num;
    

• Combining cin and cout:

  #include <iostream>
  
  int main() {
      int num;
      std::cout << "Enter a number: ";
      std::cin >> num;
      std::cout << "You entered: " << num << std::endl;
      return 0;
  }
  

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Comments

Comments are a crucial part of writing understandable and maintainable code. In C++, single-line comments start with // and extend to the end of the line. For example, // This is a single-line comment. Multi-line comments are enclosed in /* ... */ and can span multiple lines. For example, /* This is a multi-line comment */. Comments improve code readability, explain code functionality, and can be used to temporarily disable code during debugging.

• Single-line comments:
  • Use // to write comments on a single line.
  • Example:

  // This is a single-line comment
  std::cout << "Hello, World!" << std::endl;
  

• Multi-line comments:
  • Use /* ... */ to write comments spanning multiple lines.
  • Example:

  /*
  This is a multi-line comment.
  It can span multiple lines.
  */
  std::cout << "Hello, World!" << std::endl;
  

• Purpose of comments:
  • Improve code readability.
  • Explain code functionality.
  • Temporarily disable code during debugging.

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Example Program with All Concepts

• Example:

#include <iostream>

int main() {
    // Prompt user for input
    std::cout << "Enter a number: ";
    int num;
    std::cin >> num; // Read user input

    // Display the input number
    std::cout << "You entered: " << num << std::endl;

    return 0; // Program ends successfully
}

• Review:
  • Includes the #include <iostream> directive.
  • Defines the main function.
  • Uses cout for output and cin for input.
  • Contains single-line comments.

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