## Create Functions in Files

Both scripts and functions allow you to reuse sequences of commands by storing them in program files. Scripts are the simplest type of program, since they store commands exactly as you would type them at the command line. Functions provide more flexibility, primarily because you can pass input values and return output values. For example, this function named `fact` computes the factorial of a number (`n`) and returns the result (`f`).

```function f = fact(n) f = prod(1:n); end```

This type of function must be defined within a file, not at the command line. Often, you store a function in its own file. In that case, the best practice is to use the same name for the function and the file (in this example, `fact.m`), since MATLAB® associates the program with the file name. Save the file either in the current folder or in a folder on the MATLAB search path.

You can call the function from the command line, using the same syntax rules that apply to functions installed with MATLAB. For instances, calculate the factorial of 5.

```x = 5; y = fact(5)```
```y = 120```

Starting in R2016b, another option for storing functions is to include them at the end of a script file. For instance, create a file named `mystats.m` with a few commands and two functions, `fact` and `perm`. The script calculates the permutation of (3,2).

```x = 3; y = 2; z = perm(x,y) function p = perm(n,r) p = fact(n)*fact(n-r); end function f = fact(n) f = prod(1:n); end```

Call the script from the command line.

`mystats`
```z = 6```

### Syntax for Function Definition

The first line of every function is the definition statement, which includes the following elements.

`function` keyword (required)

Use lowercase characters for the keyword.

Output arguments (optional)

If your function returns one output, you can specify the output name after the `function` keyword.

`function myOutput = myFunction(x)`

If your function returns more than one output, enclose the output names in square brackets.

`function [one,two,three] = myFunction(x)`

If there is no output, you can omit it.

`function myFunction(x)`

Or you can use empty square brackets.

`function [] = myFunction(x)`

Function name (required)

Valid function names follow the same rules as variable names. They must start with a letter, and can contain letters, digits, or underscores.

### Note

To avoid confusion, use the same name for both the function file and the first function within the file. MATLAB associates your program with the file name, not the function name. Script files cannot have the same name as a function in the file.

Input arguments (optional)

If your function accepts any inputs, enclose their names in parentheses after the function name. Separate inputs with commas.

`function y = myFunction(one,two,three)`

If there are no inputs, you can omit the parentheses.

### Tip

When you define a function with multiple input or output arguments, list any required arguments first. This ordering allows you to call your function without specifying optional arguments.

### Contents of Functions and Files

The body of a function can include valid MATLAB expressions, control flow statements, comments, blank lines, and nested functions. Any variables that you create within a function are stored within a workspace specific to that function, which is separate from the base workspace.

Program files can contain multiple functions. If the file contains only function definitions, the first function is the main function, and is the function that MATLAB associates with the file name. Functions that follow the main function or script code are called local functions. Local functions are only available within the file.

### End Statements

Functions end with either an `end` statement, the end of the file, or the definition line for a local function, whichever comes first. The `end` statement is required if:

• Any function in the file contains a nested function (a function completely contained within its parent).

• The function is a local function within a function file, and any local function in the file uses the `end` keyword.

• The function is a local function within a script file.

Although it is sometimes optional, use `end` for better code readability.