# Overview

This article explains about expression in Small Basic. In Mathematics, there are three types of expression - identify, equation and definition. But in Small Basic, there are two types of expression - substitution and condition.

# Substitution

Substitution is equality which heft-hand side is a variable or a property of an object and right-hand side becomes a value. The value is assigned into the variable or the property. Following three lines are all substitutions.

`gw `

```
=
```

`598`

`GraphicsWindow`

`.`

```
Width
```

`= `

`gw`

`a `

```
=
```

`2 `

`* `

`Math`

`.`

```
Pi
```

`* `

`r`

In Small Basic, right-hand side of substitution equality is not allowed to use boolean operation (And or Or), equality or inequality.

# Condition

Condition is described in If statement or While statement. Condition is an equality, an inequality, a boolean variable, or an expression with boolean operation(s) which becomes a boolean value ("True" or "False"). In following lines, condition is (0<= x) And (x < gw) And (0 <= y) And (y <= gh).

```
If
```

`(`

`0`

`<`

```
=
```

`x`

`) `

```
And
```

`(`

`x `

```
<
```

`gw`

`) `

`And `

`(`

```
0
```

`<`

`= `

`y`

```
)
```

`And `

`(`

```
y
```

`<`

`= `

`gh`

```
)
```

`Then`

` `

```
color
```

`= `

`GraphicsWindow`

`.`

`GetPixel`

`(`

`x`

```
,
```

`y`

`)`

`EndIf`