Computer Programming is to let the computer know what we want it to execute.

Computer understands only a special language. When you want to communicate with your friends, you use human languages like english, french or spanish. When you want to communicate with a computer you use computer languages like ruby, python or clojure. All of them are examples of computer programming languages.

Enough introduction, let’s start to do some real programming.

# The 3 steps of an expression

Let’s imagine you don’t remember your table of multiplications and you want the computer to calculate `7` multiplied by `8` for you. How are you going to do that?

For that purpose, you will have to master the 3 steps of an expression:

1. First, you need to tell the computer that you want it to execute something. For that you use the parenthesis: `()`. The computer will execute for you the content of the parenthesis.

2. Then, you need to tell the computer what `operation` you want it to execute: in our case, the operation is the multiplication. The symbol for multiplication is: `*`.

3. Finally, you need to tell the computer what are the details of the `operation`. We call them the `operands`. In our case, the `operands` are `7` and `8`. The operands must be separated by one or more white spaces one from the other and one from the `operation`.

Combining all of that, we get:

``````(* 7 8)
``````

Now, modify the `operands` above and try to replace `7` and `8` by `4` and `5`.

What happened?

Did you get `20`?

Now, try to add more `operands`: for instance you could type `(* 2 3 4 6 8 2 3)`.

Try to add more white spaces between the operands, or between an operand and a parenthesis.

What results do you get?

When you talk to a friend you use sentences. When you talk to a computer, you use `expressions`.

# Exercises

If you are having difficulties with one exercise, read again the details of the 3 steps of an expression.

A. Write a program that calculates `7*8`

``````()
``````

Did you get `56`?

B. Write a program that calculates `2*3*4*5`

``````()
``````

Did you get `120`?

C. Write a program that calculates `2+3+4+5`

``````()
``````

Did you get `14`?

Send us a screenshot with your programs to viebel@gmail.com.