---
tags:
  - notes
  - programming
author: TrudeEH
draft: false
showToc: true
title: Compiling [MAKE / GCC]
---
Convert `C` code into machine code in 4 steps:
1. **Preprocessing** (Convert all preprocessor instructions: `#…`)
2. **Compiling** (Convert `C` code to machine code)
3. **Assembling** (Compile the necessary libraries)
4. **Linking** (Merge the compiled code with the compiled libraries)

## Libraries

Libraries are pre-written collections of code that can be reused in other programs. On **UNIX* systems, they are usually located in the `/lib/` and `/usr/include` directories.

### Math.h

For example, `math.h` is very useful to implement complex arithmetic operations.

```C
#include <math.h>
double A = sqrt(9);
double B = pow(2, 4);
int C = round(3.14);
int D = ceil(3.14);
int E = floor(3.99);
double F = fabs(-100);
double G = log(3);
double H = sin(45);
double I = cos(45);
double J = tan(45);
```

### Using Libraries

To use a library, we first have to include it in the `C` code.

```C
#include <cs50.h> // cs50.h library will be included.
```

Then, the library must be linked at compile time.

```Shell
gcc -o hello hello.c -lcs50
./hello
```

## Optimization Flags

- `-O2` Optimize for speed
- `-O3` Optimize for speed aggressively
- `-Os` Optimize for size
- `-Og` Optimize for debugging
- `-Oz` Optimize for size aggressively

## Make

`Make` Is a build automation tool that automates the process of compiling, linking and building executables.  
An example `Makefile` could look like the following:

```Makefile
hello:
	gcc -o hello hello.c -lcs50
clean:
	rm -f hello
```

```Shell
make #Compiles hello.c
make clean #Removes the executable (hello) generated by the make command.
```