# What is a function in Excel?

Microsoft Excel's table structure is a great way to keep organized. But the program is much more than just a series of rows and columns into which you can enter data.

Excel really becomes powerful once you start using

Functions can do many things to speed up your calculations. For example, you could use functions to take the sum of a row or column of data; find the average of a series of numbers; output the current date; find the number of orders placed by a particular customer within a given period of time; look up the e-mail address of a customer based on his or her name; and much more. It's all automatic — no manual entry required.

Let's take a closer look at functions to see how they work.

## The structure of a function

Think of a function like a recipe: you put together a series of ingredients, and the recipe spits out something totally new and different (and, in most cases, more useful, or delicious, than the thing that you put in). Like recipes, functions have three key pieces that you should keep track of:

**First, there's the**. This is just like the recipe name that you would see at the top of one of the pages of your cookbook. It is a unique identifier that tells Excel what we are trying to cook up.function name **Next, there are**. Arguments are just like the ingredients of a recipe. They're pieces that you put in that will eventually combine to make something bigger.arguments **Finally, there's the**. The output of a function is just like the output of a recipe — it's the final product that is ready to be presented to the user (or, in the case of a recipe, eaten).output

## Writing a function in Excel

When we enter functions into Excel, we use a special character to tell the program that what we are entering is a function and not a normal block of text: the equals sign (

The basic structure of a function is as follows:

=FUNCTION_NAME (argument_1 ,argument_2 ,argument_3 ...)

Output:Output

After the

We then list the

To finish writing a function, wrap up the list of arguments with the close parentheses sign (`Enter` key to complete your entry. You'll see that rather than displaying the text that you entered, Excel shows the

## A practical example

Let's look at a practical example using the

=SUM (number_1 ,number_2 ...)

To recap: the name of the function is `Enter`, Excel will show you the

Try entering the following into a cell on a blank spreadsheet:

=SUM (3 ,7 )

Output:10

Excel outputs

Here's another example with even more arguments:

=SUM (1 ,2 ,3 ,4 ,5 )

Output:15

Here, Excel outputs

## Infinite arguments and optional arguments

Throughout these pages, we'll use a couple different types of notation to denote special cases within functions:

First, some functions, like

=FUNCTION_NAME (argument_1 ,argument_2 ,argument_3 ...)

If a function has a finite number of arguments, you won't see that

=FUNCTION_NAME (argument_1 ,argument_2 )

Finally, some arguments to functions are optional, just like some ingredients of a recipe might be optional. If one or more arguments of a function are optional, we'll follow them up with an

=FUNCTION_NAME (argument_1 ,argument_2 (optional) )

In most of our function tutorials, we'll explain why something is optional and how you can use it.

That's it! Now that you know what a

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