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.

#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.

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

Then, the library must be linked at compile time.

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:

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

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