If you're not a programmer
This chapter is for people who have never written a single program in an imperative programming language. If you are used to languages likes C, C++, Python, Perl, Ruby or if you know what the words variable, constant, type, instruction, assignation mean you may (No! You SHOULD!) skip this section entirely.
How do programs work?
In the programming world there are many families of languages: functional, logic, imperative.
Go, like C, C++, Python, Perl and some others are said to be imperative languages because you write down what the processor should execute. It's an imperative way to describe tasks assigned to the computer.
An imperative program is a sequence of instructions that the processor executes when the program is compiled and transformed to a binary form that the processor understands.
Think of it as a list of steps to assemble or build something. We said "sequence" because the order of these steps generally matters a LOT! You can't paint the walls of a house when you haven't built the walls yet. See? Order matters!
What are variables?
When you solve math problems (mind you it won't be about math this time), you say that the variable x is set to the value 1 for example.
Sometimes you have to solve equations like: 2x + 1 = 5. Solving here means finding out the value of the variable x.
So it's safe to say that x is a container that can contain different values of a given type.
Think of them as boxes labeled with identifiers that store values.
What is assignation?
We assign a value to a variable to say that this variable is equal to this value from the assignation act on, until another assignation changes its value.
Assignation is the act of storing values inside variables. In the previous snippet, we assigned the value 5 to the variable whose identifier is x (we say simply the variable x) and just after, we assigned to the variable x its own value (5 is what we assigned to it in the previous instruction) plus 3. So now, x contains the value 5+3 which is 8.
What is a type?
Each declared variable is of a given type. A type is a set of the values that the variable can store. In other words: A type is the set of values that we can assign to a given variable.
For example: A variable x of the type integer can be used to store integer values: 0, 1, 2, ...
The phrase "Hello world" can be assigned to variables of type string.
So we actually declare variables of a given type in order to use them with values of that type.
What is a constant?
A constant is an identifier that is assigned a given value, which can't be changed by your program.
We declare a constant with a given value.
For example, we can declare the constant Pi to be equal to 3.14. During the execution of the program, the value of Pi won't and can not be changed. There is no assignation of values to constants.
Constants are useful to make programs easy to read and to maintain. In effect, writing Pi instead of the floating point number 3.14 in many spots of your program make it easier to read.
Also, if we decide to make the ouput of our program that uses Pi more precise, we can change the constant's declared value once to be 3.14159 instead of the earlier 3.14 and the new value will be used all along when the program is compilled again.
Imperative programming is easy. Easy as putting values in boxes. Once you understand this very basic thing, complex (notice, I didn't say complicated) things can be seen as a composition of simpler things.
Easy and fun. Fun as playing with Lego sets :)