Week 4: Pointers, Memory and 16 Digits to Work With

31 Jul 2025

German Shorthaired Pointer Dog

Well, this is not a post about a dog or dogs, but yes, it is about pointers. The nervousness with which I started Week 4 Memory, was justified. One of the instructors explicitly said that the topic of pointers was probably going to be the most challenging topic to be tackled in CS50. malloc() was lingering in my memory as I started this Week 4’s topic.

Prof. Malan brought literal training wheels to class which he threw to the ground to demonstrate things were being escalated i.e. opening the fire hose.

The highlight this week was learning about Hexadecimals (base-16). The shots video on Hexadecimal really brought me to understand the system versus the coverage in the main lecture. It brought the light-bulb moment when I saw the notation and a recall of some computer science literature I have come across , 0xADC et. al.

Learning Hard Topics

I ‘sat’ through the pointers lecture (shots) in order to get it! I was in no rush to get this topic over with, nor rush to the Problem Set to move along the course. I wanted to develop my ability/ resilience to learn difficult stuff. As Doug Lloyd pointed out

pointers take a lot of practice to master. But the benefit we get from their correct use, far outweighs the effort it takes to learn and master them.

Doug’s quick take really exposed the fundamentals of pointers and the topic sunk in. The main consolation was learning about their utility in File I/O. An area which should excite any enthusiast as it avails the programmer power to manipulate files!

Getting through Problem Set 4 was through small progressively victories, getting through one function at a time. Through it all, I got to understand nested loops and 2 dimensional arrays even better. There were a lot of those with this pset. Victory run, solving an upper limit case for the image manipulation routine, by investigating the output from the program. The correct program control and condition selection was the sticking point. More learning.

Sepia Problems - Pixel Values > 255

Taking from the lecture, I had opportunity to investigate memory issues when my code was found faulty by the check50, using Valgrind

Memory Issues

What I learnt About Pointers

• Entirely within the content of CS50, (i’m certain anywhere else,)

  Pointers are just addresses . Addresses to memory where variables live.

• Pointers allow us to pass data back and forth between functions. Overcoming the limitation of local variable scope.

• A lot of doodling with arrows helps expose the foundational concept of what is happening when dealing with pointers.

• A single pass of the topic might not be sufficient to get what pointers are all about. Several and alternative takes on the subject will most likely bring the point home. In the course there are three!