C Hello World
Lesson 1.3: Your First C Program ("Hello, World!")
It's time to write your first C program! We'll start with the classic "Hello, World!" program, a simple program that displays the message "Hello, World!" on the screen.
Writing the Code
Create a New File:
Open your code editor (e.g., Visual Studio Code) and create a new file.
Save it with a .c extension (e.g., hello.c).
Type (or Copy/Paste) the Following Code:
C
#include <stdio.h> // Include the standard input/output library
int main() { // The main function - the starting point of your program
printf("Hello, World!\n"); // Print the message
return 0; // Indicate successful program execution
}
Understanding the Code
#include <stdio.h>: This line tells the compiler to include the stdio.h (standard input/output) header file. This file contains the definition of the printf function, which we use to display output.
int main(): This is the main function, which is the heart of every C program. Execution always starts here.
printf("Hello, World!\n");: This line:
Calls the printf function.
Passes the string "Hello, World!\n" as an argument. The \n is a special character called a newline, which tells the computer to move the cursor to the next line after printing the message.
return 0;: This line ends the main function and indicates that the program has finished successfully. The value 0 is a standard return code for successful program termination.
Compiling the Code
Open a Terminal or Command Prompt: Navigate to the directory where you saved your hello.c file.
Compile with GCC: Type the following command and press Enter:
Bash or ZSH
gcc hello.c -o hello
This command does two things:
It compiles your C code (hello.c) into machine code.
It creates an executable file named hello (or hello.exe on Windows) that you can run.
Running the Program
In VS Code (with Code Runner): Press Ctrl+Alt+N to run the code.
From the Command Line: Type the following command and press Enter:
Linux/macOS: ./hello
Windows: hello or hello.exe
The Output
You should see the message "Hello, World!" printed in the terminal or command prompt window. Congratulations! You've just compiled and run your first C program.
Key Points to Remember
Every C program must have a main function.
#include <stdio.h> is needed to use input/output functions like printf.
printf is used to display output to the console.
You compile C code using a C compiler like GCC.
The compiled code is an executable file that you can run.