Introduction #

When people start with C, they usually write code by copying examples.
That works for a while, but later many errors happen simply because they don’t understand how a C program is structured and why things are written in a certain order.

C is very straightforward. It doesn’t try to help you or guess your intention.
If you follow the structure, it works. If you don’t, the compiler complains.

So let’s understand the structure properly before moving ahead.

A Simple C Program #

#include <stdio.h>

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

This is a basic and complete C program.
It prints a message and exits.

Now let’s go through it piece by piece, the way you should actually think about it.

Header File (#include <stdio.h>) #

#include <stdio.h>

This line tells the compiler that the program will use input/output functions.

printf() is not built into the C language itself.
It is declared inside the stdio.h header file.

If you remove this line and still use printf(), the compiler will either throw an error or at least a warning, because it does not know what printf is.

Simple rule in C:
If you use a function, the compiler must see its declaration first.

That’s the purpose of header files.

main() Function – Program Starts Here #

int main()
{
    ...
}

Every C program must have a main() function.

This is where execution begins.
The operating system runs your program and enters main() first.

It does not matter where main() is written in the file. Execution always starts there.

Why main() Returns int #

int main()

The return type of main() is int because the program returns a status value to the operating system.

return 0; means the program ended successfully.
Any other value usually means some error.

You may ignore this in very small programs, but it becomes important when your program is part of a script, a tool, or an embedded system.

So returning an int from main() is not optional.

Curly Braces { } – Function Body #

{
    printf("Hello, World!");
    return 0;
}

Curly braces define the body of the function.

All statements inside these braces belong to main().
Anything outside does not.

In C, braces are very important.
Most beginner mistakes come from missing or misplaced braces.

Executable Statements #

printf("Hello, World!");

This line prints text to the output screen.

printf() sends formatted output to standard output.
The semicolon ; marks the end of the statement.

In C, every statement must end with a semicolon.
Missing it is one of the most common beginner errors.

return 0; – Ending the Program #

return 0;

This line tells the operating system that the program finished normally.

Some compilers allow you to skip this line, but writing it is a good habit.
In C, being explicit is always safer.

What Happens When You Compile a C Program #

When you compile a C program, this is what happens:

First, the preprocessor handles #include statements.
Then the compiler converts C code into machine code.
After that, the linker connects required library code.
Finally, the executable file is created.

This flow stays the same for small programs and large projects.

How This Grows in Real Programs #

As programs become bigger, you will add more header files, more functions, and multiple .c and .h files.

But the basic structure stays the same:
header includes at the top,
one main() function,
and code written inside functions.

Understanding this early makes C much easier to work with.

Final Words #

C is simple, but it is strict.

It doesn’t hide things, and it doesn’t protect you much.
That’s why understanding the structure of a C program is important.

Once this is clear, learning variables, loops, functions, and pointers becomes much smoother.