Skip to main content

Hello World

It's tradition to start a programming journey in a new language by writing a simple program that prints "Hello, World!" to the screen, so let's do that:

helloworld.c
#include <stdio.h>

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

Here's a graphical breakdown of the code:

hello world visual description

The image above might seem confusing with all that text gathered together, but in reality this program is very simple. Let's analyze the code:

  • #include <stdio.h> is a preprocessor directive. It tells the compiler to include the contents of the stdio.h file, which contains declarations of standard input/output functions (like printf).
  • int main() { ... } is the definition of the main function. Every C program must have a main function, which is the starting point of execution.
    • int indicates that the main function returns an integer (the "exit code" of the program).
    • The curly braces {} delimit the body of the function, i.e., the instructions that make it up.
  • printf("Hello, World!\n"); is a call to the printf function, which prints text to the screen.
    • "Hello, World!\n" is a string literal, i.e., a sequence of characters enclosed in double quotes.
    • \n is an escape sequence that represents the newline character.
    • The semicolon ; terminates the statement.
  • return 0; is the statement that terminates the main function and returns the value 0 to the operating system. By convention, 0 indicates that the program terminated successfully.

Compiling and executing​

To compile and run this program (assuming you've saved it in a file named helloworld.c):

  1. Open a terminal/command prompt and ensure you are located in the same folder as the C file (use dir and cd commands to navigate through CLI).
  2. Type the command
    gcc -Wall -g -o helloworld helloworld.c
    and press ENTER/RETURN ⏎. What do those gcc arguments/flags mean?
    • -Wall enables all warnings (recommended).
    • -g generates debugging information, useful when using a debugger (like GDB).
    • -o helloworld specifies the name of the executable file (output).
  3. If there are no errors, an executable file named helloworld will be created.
  4. Type ./helloworld (or ./helloworld.exe on Windows) and press Enter to run the program. The ./ prefix is necessary to tell the shell to look in the current directory for the executable file.

You should finally see "Hello, World!" printed on the screen.

Note

If you open the .exe file manually from File Explorer, it will probably close immediately. This is because return 0; terminates the program without leaving it open for us to read the message.

You can prevent the program from closing immediately by adding getchar(); before the return:

helloworld.c
#include <stdio.h>

int main() {
    printf("Hello, World!\n");
    getchar(); // prevent terminal from closing
    return 0;
}
Last updated on