Chapter 1: Learning C Programming with ChatGPT: ‘Hello, World!’

The article was created based on a response from ChatGPT 4.0 Mini, which explained how to teach beginners C programming using the “Hello, World!” program. The content has been edited and supplemented where necessary to enhance clarity.

この記事はChatGPTと学ぶC言語① “Hello, world!”の英訳版です（おためし）．

Let’s try outputting ‘Hello, World!’

Let’s first take a look at the basic program in C that displays “Hello, World!” on the screen.

#include <stdio.h>

int main(void) {
    printf("Hello, World!\n");
    return 0;
}

This code is the most basic “Hello, World!” program in C. I will explain each part clearly.

#include <stdio.h>

This is called a preprocessor directive, and it is an instruction to add commonly used standard libraries to the program in C. Specifically, stdio.h is a library used for handling standard input and output, and it enables the use of functions like printf().

• stdio stands for “Standard Input/Output,” and it contains many functions used for interacting with the computer, such as reading from and writing to the console or files.
• #include is an instruction to include external code. Without this directive (#include <stdio.h>), you wouldn’t be able to use the printf() function in your program.

int main(void)

This is called the main function. In C programs, execution always begins from this main() function.

(Supplement 1) ChatGPT outputted int main(), but in C, int main(void) is considered safer. In C++, both are considered to have the same meaning.

• int means “integer type.” Here, it indicates that the function will return an integer value (such as 0).
• main() is the function name, and the execution of the program starts from here. Inside the function, the code for the tasks you want the program to perform is written.
• (Supplement 2) The contents inside the function’s parentheses are called arguments, and the argument void indicates that no arguments are required for the function.

printf("Hello World!\n");

• printf is a standard output function used to display messages on the screen. In this example, it is used to display the string “Hello, World!”.
• \n is a newline character. Using it causes a line break after the message, so the next output starts on a new line.
  • If \n is not written, the message will be displayed on the screen, and the next output will continue on the same line.

return 0;

• return is an instruction to exit from the function.
• 0 is a value returned to indicate that the program has terminated successfully. In many programs, return 0; is used for this purpose.

Here is the flow of the program.

1. #include <stdio.h>:
   • Loads the necessary library (standard input/output library).
2. int main():
   • The program starts from the main() function.
3. printf("Hello, World!\n");:
   • Displays “Hello, World!” on the screen.
4. return 0;:
   • Ends the program normally.

Execution Method (Compilation and Execution)

To run a C program, a process called compilation is necessary. Using a compiler, the source code is converted into a format that the computer can understand. Below are the general steps.

1. Write the Program
   • For example, save the code in a file named hello.c.
2. Compile the Program
   • To compile, enter the following command in the command line (terminal) using the GCC compiler:

gcc hello.c -o hello

(Supplement 3) Alternatively, you can write the command as follows:

gcc -o hello hello.c

3. Run the Program
   • After the compilation is successful, run the program with the following command:

./hello

(Supplement 4) Alternatively, you can combine the compilation and execution into one command:

gcc -o hello hello.c && ./hello

4. Result
   • The message “Hello, World!” should be displayed on the screen.

Summary

• #include <stdio.h>: Includes the library for standard input/output.
• int main(void): The entry point of the program, the main function.
• printf("Hello, World!\n");: Displays the message on the screen.
• return 0;: Indicates the program has ended successfully.

By understanding this simple program, you can grasp the basic syntax and flow of a C program. As the next steps, it’s good to learn about variables, operators, and control structures (such as if statements and for loops).

C is a simple yet powerful language. By writing and running code, you’ll continue to improve your skills.