Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Update pointers.md #1

Open
wants to merge 1 commit into
base: main
Choose a base branch
from
Open

Update pointers.md #1

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
8 changes: 4 additions & 4 deletions pointers.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -122,7 +122,7 @@ Because the storage for variables can occur anywhere in memory, a pointer-to-`X`

Almost all of today's computers have more than $10$ gigabytes of memory. Consider the tablet computer on which I am penning this column -- it has $32$ GB of RAM! In order to uniquely identify every byte of memory on my tablet, I would need $34,359,738,368$ values. Now, here's the math!

The computer can only handle $1$s and $0$s. So, how can you use those two values to represent decimals? Let's assign $1$, $2$, $3$, $4$, $5$, ... to a unique combination of a sequence of $1$s and $0$s. For example,
The computer can only handle `1`s and `0`s. So, how can you use those two values to represent decimals? Let's assign $1$, $2$, $3$, $4$, $5$, ... to a unique combination of a sequence of `1`s and `0`s. For example,

$$
0000 = 0 \\
Expand All @@ -143,15 +143,15 @@ $$
1111 = 15 \\
$$

Count up the lines above and note that there are 16 unique combinations possible of 4 `1`s/`0`s that can be used to represent the numbers $0$ through $15$. Mathematically, for a sequence of $n$ 1s and 0s, there are $2^n$ different combinations (e.g., $2^4=(2*2*2*2)=16$). So, in order to represent $34,359,738,368$ (the number of bytes of memory that my computer holds!) we would need
Count up the lines above and note that there are 16 unique combinations possible of 4 `1`s/`0`s that can be used to represent the numbers $0$ through $15$. Mathematically, for a sequence of $n$ `1`s and `0`s, there are $`2^n`$ different combinations (e.g., $`2^4=(2*2*2*2)=16`$). So, in order to represent $34,359,738,368$ (the number of bytes of memory that my computer holds!) we would need

$$
2^n = 34359738368\\
n = log_2(34359738368)\\
n = 35
$$

$35$ $1$s and $0$s. Because that's oddly specific to my tablet and computer scientists like to make things future-proof, they specified that sequences of $64$ $1$s/$0$s are better for representing addresses of bytes in memory! That's why they say that modern computers are so-called _64-bit computers_ as opposed to the 32-bit computers of the late 1990s. Every $1$/$0$ combination is represented in hardware by a bit and, remember, there are $8$ bits per byte. So a pointer-to-`X`-type variable occupies $64 / 8 = 8$ bytes of space! How cool is that?
$35$ `1`s and `0`s. Because that's oddly specific to my tablet and computer scientists like to make things future-proof, they specified that sequences of $64$ `1`s/`0`s are better for representing addresses of bytes in memory! That's why they say that modern computers are so-called _64-bit computers_ as opposed to the 32-bit computers of the late 1990s. Every `1`/`0` combination is represented in hardware by a bit and, remember, there are $8$ bits per byte. So a pointer-to-`X`-type variable occupies $64 / 8 = 8$ bytes of space! How cool is that?

## Reassigning Pointers
Remember the program from above:
Expand Down Expand Up @@ -316,4 +316,4 @@ ptr_to_int = &fived;

Can you see why?

As you continue to learn more about pointers, you will see additional common mistakes! For now, revel in your newfound power!
As you continue to learn more about pointers, you will see additional common mistakes! For now, revel in your newfound power!