[中文版本](/posts/c教程/zh-CN/01-入门/003-Writing and Running Your First Program)

Now that your compiler is ready, it’s time to write your first real C program. This is where the magic happens, you’ll write plain text, compile it into machine instructions, and watch your computer follow your commands exactly.

C doesn’t hide what’s happening under the hood. Every step, writing, compiling, linking, running, is visible and under your control.

Tiny Code

Create a new file namedhello.c and type this code:

#include <stdio.h>
int main(void) {
    printf("Hello, world!\n");
    return 0;
}

Then, compile and run it:

gcc hello.c -o hello
./hello

You should see:

Hello, world!

Breaking It Down

#include <stdio.h> This tells the compiler to use the Standard Input/Output library, which provides theprintf function.

int main(void) Every C program starts with amain function. It’s the entry point, where execution begins.

printf("Hello, world!\n"); This prints text to the screen. The\n means “newline,” so the next output starts on a new line.

return 0; Whenmain returns 0, it tells the operating system that your program finished successfully.

Why It Matters

Your “Hello, world” may look simple, but it represents an entire process:

1. The compiler translates your text (hello.c) into object code (hello.o).
2. The linker combines that code with standard libraries.
3. The executable (hello) is pure machine instructions.
4. The operating system loads and runs it.

Understanding this flow is what makes C special, it’s not just about writing code, but about knowing how code becomes software.

Try It Yourself

Change the message to"Hello, C learner!" and recompile.

Add another line:

printf("This is my first C program.\n");

Try leaving out the semicolon, what error does the compiler show?

Try removing#include <stdio.h>, what happens then?

Experiment and break things. Every error teaches you how C thinks.

You’ve just written and run your first C program, a direct conversation between you and the machine. From here, every new piece of code builds on this simple moment of control and understanding.