Cs50 library on c

[Mrminime]

Good day,
I am new to Ubuntu as new to c programing. Now i am watching cs50 videos to understand better about c and cs all together.
I tried to install this by using these guide lines:


Debian, Ubuntu

First become root, as with:

sudo su -

Then install the CS50 Library as follows:

apt-get install gcc
wget http://mirror.cs50.net/library50/c/library50-c-5.zip
unzip library50-c-5.zip
rm -f library50-c-5.zip
cd library50-c-5
gcc -c -ggdb -std=c99 cs50.c -o cs50.o
ar rcs libcs50.a cs50.o
chmod 0644 cs50.h libcs50.a
mkdir -p /usr/local/include
chmod 0755 /usr/local/include
mv -f cs50.h /usr/local/include
mkdir -p /usr/local/lib
chmod 0755 /usr/local/lib
mv -f libcs50.a /usr/local/lib
cd ..
rm -rf library50-c-5



I used it, and i think everything went as planned, but as soon as i try to run gcc demo.c i get fatal error message
this error:
adder.c:2:18: fatal error: cs50.h: No such file or directory
#include <cs50.h>

So as it seems that somewhere something went wrong and I don't really know how to fix it, could anyone guide me a little bit how to fix it or how reinstall everything that c automatically would include that library?
Thanks