Training and Instructional Design

In this episode, we’ll finish looking at the integer math operators, and talk a bit about how to count by one and two using increment operators.

Welcome back to Kinderswift. Let’s continue from where we left off last time.In our last session, we used the let and var statements.

let and var statements are called definitions since they define the identifier and some information about the identifier. Once we do that we can use the identifier without var in an assignment. In a definition we do a special assignment called initializing which sets the first value of an identifier. For a constant, this value will be the only value.

Last time we used assignment to add the current value of `myResult`

and assign a new value to `myResult`

.

There is a special case of this we call an increment. The basic increment is this:

`myResult = myResult + 1`

We take `myResult`

, add one and assign it back for a new `myResult`

. We will use increments for counting. There are other ways to do the same thing. Type

` myResult += 1`

The `+= `

operator increments for us by the value on the left side of the equals. So here we increment by 1. It is the same as writing what we did just above. We can change the increment as well. If we wanted to increment by 2, we can write this:

`myresult`

+= 2

Which is the same as

`myresult = myresult + 2 `

There is one way even simpler. That is the `++`

operator. this always adds 1 to the value, but we need no equal sign.

++myResult

Increments `myResult`

by one and then shows the value of `myResult.`

You can put the plus plus at the end too, but this get a little tricky.

`myResult++`

Shows the result and then increments the value. In the playground, We need to show the result again.

and then we see the increment.

That is not all we can do. we can subtract, multiply, and divide as well. for example

`myResult = myNumber - myOtherNumber`

Subtracts `myNmber`

from `myOtherNumber`

.

We use an asterisk for multiplication so:

`myResult = myNumber * myOtherNumber`

multiplies `myNumber`

by `myOtherNumber`

.

We use a forward slash to divide. Try

`myResult = myNumber / myOtherNumber`

.

This divides `myNumber`

by `myOtherNumber`

giving an integer result.

Let’s use some literal numbers to see why this is important :

Dividing four by 2 gets us two as expected.

Dividing five by two also gets us two, since we are using integers. The remainder gets cut off.

So far I’ve kept the examples whole numbers. Try this:

`myResult = 2 - 4`

We get a negative number for a result. We can use negative numbers in calculations as well. This subtraction is the same as

`myResult = 2 + -4`

Which brings up a possible error you might get. Be careful with spacing. type this:

`myResult = 2 + -4`

We get an error since Swift thinks this reads `myResult`

equals 2 negative 4. It wants an operator, not two numbers. Add a space between the minus and the 4.

`myResult = 2 + -4`

The error disappears.

Now try this: ` myResult = 1/4`

We get a result of 0. So far we are only working with integers. Like 5 / 2 above, any non integer part of division is dropped off. If we need the remainder, often called a *mod* in Computer jargon we use the % sign. So `1 % 4`

equals 1. and `5 % 2`

also equals 1.

There are a few times we use a mod for calculations. Most of the time, I want 5 divided by two to be 1.5 and one divided by four to be 0.25. That requires something else called a Double, and that will be the topic for our next lesson.

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