> ## Documentation Index
> Fetch the complete documentation index at: https://aspect.build/llms.txt
> Use this file to discover all available pages before exploring further.

# Running a “hello world” application

> Write and run a simple C hello world program with Bazel, declaring a cc_binary target and executing it with bazel run for your first C/C++ build.

To start with, let’s get the simplest possible program to execute.

<Note>
  🤔

  We’ll largely follow along with [https://bazel.build/start/cpp](https://bazel.build/start/cpp) in this lesson.
</Note>

Let's create a simple hello world application that prints “hello” to the standard out. Put this content in `src/hello.c`:

```cpp theme={null}
#include <stdio.h>

int main(int argc, char const *argv[])
{
    printf("hello world!");
    return 0;
}
```

The natural next step here is to invoke a compiler like `gcc` or `clang` to get a executable binary by invoking it with something like `gcc main.c -o main`  and run the `./main`. Under other build tools, you’d write something that performs these steps directly.

For example in a `Makefile`, it would look like this and in order to build it, one would have to invoke `make main` :

```makefile theme={null}
main: 
	gcc hello.c -o hello
```

Bazel is similar to make in this regard, however in Bazel there is no direct invocation of the compiler. Instead we use plugins (called “rules”) to describe the compilation units. For C and C++, `cc_binary` is the rule for turning `.c` code into executable binaries. Put this content in `src/BUILD`:

```python theme={null}
cc_binary(
	name = "main",
	srcs = ["hello.c"]
)
```

Running this main.c is similar to make, running `bazel run src:main` will compile and run `hello.c`.

This build will depend on a hermetic LLVM toolchain, which you’ll observe downloaded and extracted the first time you run a build.

<Note>
  Bazel builds should ideally be completely reproducible across machines, regardless of OS distro, installed system libraries, and so on.
  Every file or tool needed for the build is managed by Bazel. This property is called “hermeticity”.
</Note>

<Callout icon="book">
  Read more: [hermetic c toolchain](/blog/hermetic-c-toolchain)
</Callout>

If there is an existing Makefile in your repository, there’s no reason to remove it. Instead, adjust it so that it runs bazel. This avoids re-training engineers and triggering their aversion to change.

```makefile theme={null}
main:
	bazel build //:main
```