Pattern catalog

Patterns are common ways of doing things, like recipes. People have patterns for solving equations, making web pages, wrapping gifts, all sorts of things. Part of learning a skill is learning the patterns that help you be more effective.

Here are patterns on this website. This list can help you find the patterns you need to do a task.

Name	Situation	Tags	Action	Where referenced
Accumulator	You have a data set, and you want to total up or count the values.	Loop	Loop over a data table. For each record, add a field to a total, count, or whatevs. Needs: A data set. Provides: A variable with a total or count.	Processing a Range, Data tables, Validate then process
Create a Range	You have a set of records in a worksheet that you want to process.	Range	`Set rSomething = Range(top left cell, bottom right cell)` Needs: A worksheet with records in it. Provides: An object that you can loop across.	Ranges
Find smallest/largest values	You have some records in a `Range`.	Range, Loop	Loop across some records. Put an `If` in the loop, comparing the current value with the smallest/largest so far. Needs: You want the smallest and/or largest value(s) for a field in the records. Provides: Smallest/largest values.	Min and max
Flag	You have a bunch of code. You want to see whether something happened in the code. It could happen in more than one place in the code. Validation is a common example, where user input could be invalid in a number of different ways.	Validation, If	A variable that summarizes the results of a bunch of code. Needs: A variable you can use as a flag. Provides: A value in the flag, that you can test for.	Validate then process, Range validation, Basic validation: strings, Better validation
Guard pattern	Your program could do something stupid, like try to divide by zero.	If	Prevent your code from doing something crazy. Needs: Some data to test. Provides: Usually an error message.	Validate then process, Guard pattern
Hungarian variable names	You need to name some variable names.	Variables	"Sales tax rate" is `sSalesTaxRate`. Price is just `sPrice`. Needs: A cell in a worksheet. Provides:	Easy is good
Input from a cell	You want to get one data value from the user.	Input	Get input from a cell. Needs: A cell in a worksheet. Provides: A variable with a value.	Generalize
Input from a dialog	You want to get one data value from the user.	Input	Use a dialog to get some input. Needs: A human to type a value into a dialog, and/or read a value from a dialog. Provides: A variable with a value.
Input-processing-output	Data needs to be transformed into other data.		A program inputs data from somewhere, does computations with the data, and outputs the result. Needs: Provides:	Generalize
Multiway	A variable has one of several distinct values, like different colors ("red", "green", or "blue"), or different ranges (1 to < 10, 10 < 30, ...). You want to do different things, depending on the value.		Use a chain of `If` statements. Needs: A variable with several distinct values or ranges. Provides: Different program states, depending on the variable's value.	Basic validation: strings, Multiway