# CS 105

## Review: Variables

Variables store data in a computer's memory for later use.

All data in a variable has a data type.

## Numbers

```var n = 42;
var m = 4.2;
var o = 0.42;
```

## Strings

```var s = "Hello, world!";
var t = "ILLINOIS";
var u = "14";  // 14, as a String
```

## Functions

```var f = function(arg1) {
return (arg1 + 1);
};
// Function call: f(3)

var g = function(arg1, arg2) {
return arg1 * arg2;
};
// Function call: g(4, 5)
```

## Arrays

```var a = [1, 2, 3, 4, 5];
var b = ["Hello", "World"];
var c = [10, "after", 11, "o'clock"];
```

## If Statements

```var x = getSomeValue();
if (x < 10) {
...
}
```

## If Statements

```var x = getSomeValue();
if (x < 10) {
...
} else {
...
}
```

## For Loops

```for (var i = 0; i < 10; i++) {
...
// Runs 10 times
...
}
```

## Functions

```var f = function(a, b, c, d) {
...
};
```

## Puzzle #1

```var d = 0;
for (var i = 0; i < 5; i++) {
d = d + i;
}
```
A) 0
B) 5
C) 10
D) 15

## Puzzle #2

```var k = 17;
var a = [3, 4, 5];

for (var i = 0; i < a.length; i++) {
k = k – a[i];
}
```

A) 2
B) 3
C) 4
D) 5
E) 6

## Puzzle #3

```var cart = [ 8.50, 52.49, 31.99 ];
```

Get _____% off orders of \$ __________ or more!

OR

Get _____% off orders of \$ __________ or more!

## Puzzle #3

```var calculate = function (cart) {

}
```

## Dot Operator

```console.log("Hello, world!");
```

## Dot Operator

```var s = "Hello";
var l = s.length;     // 5
var c = s[1];         // "e"
var c2 = s.charAt(4); // "o"

var a = [2, 4, 6, 8, 10];
var len = a.length;  // 5
var n = a[2];        // 6
```

## Puzzle #4

```var s = "Hello, world!";
var x = s.length;
```

## Puzzle #5

```var a = [2, 4, 6, 8, 10];
var y = a.length;
```

## Puzzle #6

```var s2 = "Hello, world!";
var z = s2.charAt(4);
// Same as s2[4]
```

## Place Value of 123

```  102 = 100  |  101 = 10  |  100 = 1
-------------|------------|----------
Place        |            |
Value:  100  |        10  |        1
|            |
Digit:    1  |         2  |        3

+            +
```

## Place Value of 213

```  102 = 100  |  101 = 10  |  100 = 1
-------------|------------|----------
Place        |            |
Value:  100  |        10  |        1
|            |
Digit:    2  |         1  |        3

+            +
```

## Our Number System

Our number system uses the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9. We call this system base 10 or the decimal number system.

Computers use the digits 0 and 1. We call this system base 2 or the binary number system.

## Place Value of 1012

```   22 =      |   21 =     |   20 =
-------------|------------|----------
Place        |            |
Value:       |            |
|            |
Digit:    1  |         0  |        1

+            +
```

## Place Value of 0112

```   22 =      |   21 =     |   20 =
-------------|------------|----------
Place        |            |
Value:       |            |
|            |
Digit:    1  |         0  |        1

+            +
```

## Bits and Bytes

We call a single binary digit a bit.
It stores either the value 0 or 1.

## Byte

Eight bits make up one byte.

0000 00002 == 010

1111 11112 == 25510

## Application

In a computer, colors are represnted by an array of three bytes: red, green, and blue.
(Primary colors of light)