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## Chapter 10 – Random Numbers

### RANDOMIZE, RND and % RND

This chapter deals with the functions **RND**, **RND ()** and **% RND** and the keyword **RANDOMIZE**. They are all used in connection with random numbers, so you must be careful not to get them mixed up.

As far as normal functions go, **RND** is quite unusual: although it does calculations and produces a result, it does not need an argument.

Each time you use it, its result is a new *random floating point number* Sbetween **0** and **1**. (Sometimes it can take the value **0**, but never **1**.)

Try:

```
10 PRINT RND
20 GO TO 10
```

to see how the answer varies. Can you detect any pattern? You shouldn't be able to; *random* means that there is no pattern[^p64-1].

**% RND**, which is – as seen on *Chapter 8* – the version of **RND** available in integer expressions, behaves slightly differently. It takes a single argument (e.g. *n*) and returns a random integer in the range **0** to **n-1**. For example, **%RND 10** will return a random integer between **0** and **9**.

While **RND** returns, as discussed above, a random number between **0** and **1**, you can easily get random numbers in other ranges. For instance, **5\*RND** is between **0** and **5**, and **1.3+0.7\*RND** is between **1.3** and **2**. For cases where we need to be in the standard expression evaluator, there is yet another version of **RND**, which is not an integer expression only function:

**RND** (*n*)

which returns a random integer between **0** and **n-1** like **%RND n**. This is recommended over using the standard fractional floating-point function **RND** since it doesn't suffer from the biasing inherent in converting a fractional random number to an integer with multiply and truncation steps.

To get whole numbers with **RND** use **INT** (remembering that **INT** always rounds down) as in **1+INT (RND\*6)**. If however your desired random values can stay within the range of **0** to **65535,** it is better to use **% RND or RND()** which avoid the unnecessary conversions – and rather slow – floating point calculations involved.

To illustrate better what all version can do, let's use all three of them in a program to simulate dice throwing. **RND\*6** is in the range **0** to **6**, but since it never actually reaches **6, INT (RND\*6)** is 0,1,**2**,**3**,4 or **5**.

Here is the dice throwing program:

```
10 REM dice throwing program
20 CLS
30 FOR n=1 TO 2
40 PRINT 1+INT (RND*6);" ";
50 NEXT n
60 INPUT a$: GO TO 20
```

[^p64-1]: *Actually, RND is not truly random, because it follows a fixed sequence of 65536 numbers. However, these are so thoroughly jumbled up that there are at least no obvious patterns so we say that RND is pseudo-random.*