Variables 101: Knowing Your Computer

Sadly I have seen that not many want to learn to program this 2018 🙁 but even if I had only read my previous article a person and after a little time is able to send a commit to a free software project, I would be satisfied with my work 🙂

For those who love security, I promise you that the following will be a post about security todos so everyone is happy, if anyone wants to learn something else (like git, server administration, or I don't know: p), or to comment on some other topic that cannot be answered in a simple way in the comment box, let me know and we see how we can work it 😉

Well, now if we go to our thing, previously we talked about typing, and that this had to do with the way in which we save our variables in a program, now we are going to review a bit of what happens inside and hopefully it can be clear enough.

Bits

I think this is a topic that I always touch when I write about programming, it is certainly something that fascinates me and that has helped me understand many things, now I will try to explain a little how they are, how they are read, and what they are for 🙂

Think of a light switch, when the circuit is closed, we have a 0 on the screen, when we change the position of the switch, because a 1🙂 simple isn't it?

Now a 0 or with a 1 They can mean many things, it all depends on the creativity with which you take it, suppose I want to know if someone is going to the North or the South, 1 can mean north and 0, sur 🙂 let's say I want to know if someone is a man or a woman, 1 it can be a man and 0, woman 🙂. Now I want to know if this person is young or old (> 22), 0 can mean young and 1, higher. Let's keep imagining… Do you have any pets? 1 I would say yes, while 0 I'd say no Now I want you to read the following line with me:

1001

This is the short way to say ...

Una jóven mujer de no más de 22 años se dirige al norte acompañada de su mascota.

which is very different from:

0110 o Un hombre con más de 22 años de edad se dirige solo hacia el sur.

Bytes

Now let's go one step further, let's learn how to read bytes. A byte is the sequence of 8 bits, which are read from right to left and each 1 represents a power of 2 raised to the n where n is the position of the bit. As it sounds like Chinese, let's put a little example 🙂

01001011 We have this byte, now we are going to go from right to left (<-) I am going to put them from top to bottom to be able to write their meaning:

1: the bit when in position 0 indicates that we have the following 2 raised to zero or 2^0. This well we know is equivalent to 1.

1: the second bit, now the position 1: 2^1 which is the same as saying 2

0: third bit ... this should be 2^2, but since it is not on, we are going to leave it on 0

1: fourth bit, 2^3 u 8 : )

0: the same as 0

0: other 0

1:now we are in 2^6 o 64

and finally 0 , we already know what it means 🙂 now we are going to add our results and compare them with the following table 🙂 We have a 75 so let's look for it in the column Decimal and we will see what appears in Char

We have one K!! Congratulations, you already know how to read in binary 🙂 But the most sagacious may have noticed that we have also obtained a decimal number, and that it has a limit (when all values ​​are 1) That limit is found in the number 255.

Word

Now more than one will tell me, but what if I need a number greater than 255? or where can I find other characters like the Japanese? Well the answer is simple, let's put together 2 bytes. Now that we have two, the possible number of combinations we have is 2^16 o 65536 possible outcomes, such as 0 is one of those, the maximum possible is 65535. Does that number ring a bell to anyone? Remember the maximum number of ports on a linux system? I leave them homework 😉

Double word & quad word

For the more mathematical there are also specific formats, the double-word contain, as many may have already imagined 2 word o 4 bytes (o 32 bits) of information, the same as saying:

11111111111111111111111111111111 or 0 a 4 294 967 295

At this point many will wonder what happens with negative numbers, that is, somewhere they must be contemplated, right? In order to be able to store a negative number, the processor developers chose to occupy the first bit on the left as a sign value. This means that if the first bit is 0 we are talking about a positive number, but if it is 1 we have a negative. Now see why the bits are so special, they can be whatever you want 😀

But this obviously leaves us with one less position to do the multiplication! So our0 a 4 294 967 295 becomes:

-2,147,483,648 a +2,147,483,647

Now, many of us already have 64 bits, and this is the value of a quad word, we can have values ​​ranging from 0 a 18 446 744 073 709 551 615. That is a big number 🙂

Why 8 bit?

This is something that more than one may be wondering, and the answer is in the hardware. From the beginning, processors needed data to be able to perform operations. The data is stored in the memory of the computer and every time the processor requires it, it uses the data buses to get it. In ancient times, these buses could communicate a maximum of 8 bits per cycle, this means that the maximum and most efficient way of moving data, was grouping 8 bits and sending them to the processor.

With the passage of time, until today, processors have developed the ability to move 16 bits, 32 bits and… 64 bits.

What does it have to do with typing?

We are now at the part where it all makes sense 🙂 Typing is a property that programming languages ​​use to name these memory spaces. All variables have their counterpart in one of these types of data, no matter what they are called. These are known as primitive data typesEach strongly typed language has its conception of these values, and the quantity they represent. For example in C we have the library limits.h which shows us the maximum and minimum amount of primitive values.

Let's see what happens if we try to break one of the values:

On the right we have the values ​​of the file limits.h and on the left we have taken one of these values ​​(unsigned short int) and we have assigned a number higher than the corresponding one. As a result the compiler warns us that we are misusing memory because the binary form of 66666 cannot fit in the binary form of 65535. This leads us to a lesson in performance when we program, if your value is not going to grow much over time, or if you do not require values ​​as large as those of a double o quad wordUsing the correct type reduces the amount of memory requested by the CPU, which implies a higher data retrieval speed if it is well calculated.

On the interpreter side this is easier due to the implicit conversions. Chen we define a variable in languages ​​such as javascript or Python, the interpreter is in charge of understanding what type it is, and allocating enough memory space to perform the operations. Let's see a simple example 🙂

As you can see, we don't have to explain to the python interpreter the type of our variable, because it is in charge of assigning a type and storing it in memory 🙂

Know your variables

This depends on the language and type of implementation that you are going to use, but the first step to be able to program is to learn the variables that you can use 🙂 Once you understand the variables, you will be in a position to use them efficiently and logically to store information (provided by a user or by the system). This is the first step on the programming ladder, and hopefully after reading this article, you will have a better understanding of how your computer works and how it stores information. It will be with me until the next article, remember to leave your comments to see if you have to reinforce or comment on any specific point. Cheers