Lesson 19 - Formatting Strings

Tutorial Series: Free C# Fundamentals via ASP.NET Web Apps

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This lesson will cover how to format strings. We already looked at how to concatenate strings, with the “+” and “+=” operators, but this lesson will show you how to handle special formatting conditions, such as the patterns seen in things like phone, social security, or credit card numbers. These all have some form of patterned formatting, or otherwise have some special arrangement of numbers and characters.

Step 1: Create a New Project

We’ll demonstrate this with a very simple loan application form that stores pieces of information like the phone number, social security number, salary and date. It will then display all of this information back to resultLabel with special formatting so that it looks presentable. Begin this lesson by creating a new ASP.NET project called “CS-ASP_019,” and set up a Default.aspx with the following Server Controls, and programmatic IDs:

  1. nameTextBox

  2. phoneTextBox

  3. ssTextBox

  4. loanDateCalendar

  5. salaryTextBox

  6. submitButton

  7. resultLabel



The first thing we will want to do is take the applicant's name that was input via nameTextBox, and output it within a formal “thank you” statement:


Step 2: String Formatting with string.Format()

This approach uses the string concatenation technique we have become familiar with. This will get the job done, but isn’t as readable owing to the multiple uses of the concatenation operator. A much more readable way of achieving this is by calling the string.Format() method instead:


This method takes in (1) a literal string argument, along with a (2) variable string argument, and then using a (3) special placeholder it transposes the variable string argument into the placeholder position within the literal string:


Note: This placeholder system is zero-based, meaning that the first value passed in will be {0}, then {1}, {2} {3}, etc.

The output when running the application will look like this:


This essentially produces a string “template” with as many placeholders as needed:



The problem now is that the entered number itself should be formatted to look more like a typical Social Security number. We start by converting this value to an integer using int.Parse(), and then storing it into an integer variable:


Step 3: Applying Special Formatting Patterns to the Placeholder

Modify the string.Format() method to take this int value and apply to it a formatting pattern of number sequences delimited by dashes. Here we took the {1} placeholder and appended to it a formatting pattern, with a colon separating the placeholder from its pattern:


The formatting pattern will become much more apparent when running the application:


Tip: You should note that phone numbers are at least 10 digits in length, which reaches the upper-limits allowable for storage into an int variable. If the first digit in the phone number is greater than 1, there is a good chance it will cross the allowable threshold and return an error. To fix this, you can store the number into a long. However, if the application ends up processing thousands of numbers (or more) this could be very inefficient and you would probably want to leave the phone number as a string.

Step 4: Inserting HTML into the Output String

You can also inject HTML straight into the output string, considering that the output is ultimately being delivered through the browser. Here, we injected a simple HTML line break tag “<br />” to put each phrase onto its own line:



Step 5: Breaking Up Code on Separate Lines for Readability

Now, let’s apply the same principles towards formatting the phone number. Add a third placeholder, {2}, which will take the value supplied in yet another argument, phone. We will be applying this process over and over again, to handle the other user inputs, which will lead to a very long statement. To make it more readable, we can use the concatenation operator to break up the statement on separate lines:


The end result will look like this:


Tip: This goes back to the previous lesson on code style. This is very subjective - what looks good to one person, may not look good to another. Here’s a good rule of thumb: keep lines approximately within an 80-column range. You can find the column number for each line at the bottom right of Visual Studio. Also, when separating lines, try to keep a logical separator in mind. Here, the <br /> tag is used as a line separator, as well as the comma after each string argument. This sets a pattern that makes it easier for you to get a sense of what the code is doing, at a glance.

Step 6: Applying Special Date Formatting

Next we will want to format the date returned by the applicant’s Calendar selection. We already saw built-in formatting methods like ToShortDateString(), but sometimes that isn’t flexible enough to handle a particular formatting requirement. Below is a short list of available date formatting options in C#:


This is a partial list that can be found by visiting:


Here we are applying some of these special date formatting rules to the fourth placeholder at {3}, which formats the date given by loanDateCalendar.SelectedDate:


This produces the date formatting shown here:


Step 7: Applying Special Currency Formatting

When working with currency you can place a “C” after the colon, inside the placeholder, to tell the compiler that this is to be formatted as a currency. If you want to allow for cents, you need to first convert the entered value to a double, as well:



For more information on currency formatting options, visit the following page showing you a variety of ways to represent exponential values, fixed point, and other numeric types of values:


Formatting strings is very useful and powerful for you, the developer, when creating forms for users to fill out. Keep these tools in mind, as they are going to be utilized in the next Challenge coming up very soon.

Related Articles in this Tutorial:

Lesson 1 - Series Introduction

Lesson 2 - Installing Visual Studio 2015

Lesson 3 - Building Your First Web App

Lesson 4 - Understanding What You Just Did

Lesson 5 - Working with Projects in Visual Studio

Lesson 6 - Simple Web Page Formatting in Visual Studio

Challenge 1

Solution 1

Lesson 7 - Variables and Data Types

Lesson 8 - Data Type Conversion

Lesson 9 - Arithmetic Operators

Lesson 10 - C# Syntax Basics

Challenge 2 - ChallengeSimpleCalculator

Solution - ChallengeSimpleCalculator

Lesson 11 - Conditional If Statements

Lesson 12 - The Conditional Ternary Operator

Challenge 3 - ChallengeConditionalRadioButton

Solution - Challenge Conditional RadioButton

Lesson 13 - Comparison and Logical Operators

Lesson 13 Challenge - First Papa Bob's Website

Solution - Challenge First Papa Bob's Website

Lesson 14 - Working with Dates and Times

Lesson 15 - Working With Spans of Time

Lesson 16 - Working with the Calendar Server Control

Challenge 4 - Challenge Days Between Dates

Solution - Challenge Days Between Dates

Lesson 17 - Page_Load and Page.IsPostBack

Lesson 18 - Setting a Break Point and Debugging

Lesson 19 - Formatting Strings

Challenge 5 - Challenge Epic Spies Assignment

Solution - Challenge Epic Spies Assignment

Lesson 20 - Maintaining State with ViewState

Lesson 21 - Storing Values in Arrays

Lesson 22 - Understanding Multidimensional Arrays

Lesson 23 - Changing the Length of an Array

Challenge 6 - Challenge Epic Spies Asset Tracker

Solution - Challenge Epic Spies Asset Tracker

Lesson 24 - Understanding Variable Scope

Lesson 25 - Code Blocks and Nested If Statements

Lesson 26 - Looping with the For Iteration Statement

Challenge 7 - Challenge For Xmen Battle Count

Solution - Challenge For Xmen Battle Count

Lesson 27 - Looping with the while() & do...while() Iteration Statements

Lesson 28 - Creating and Calling Simple Helper Methods

Lesson 29 - Creating Methods with Input Parameters

Lesson 30 - Returning Values from Methods

Lesson 31 - Creating Overloaded Methods

Lesson 32 - Creating Optional Parameters

Lesson 33 - Creating Names Parameters

Lesson 34 - Creating Methods with Output Parameters

Challenge 8 - Challenge Postal Calculator Helper Methods

Solution - Challenge Postal Calculator Helper Methods

Mega Challenge Casino

Solution - Mega Challenge Casino

Lesson 35 - Manipulating Strings

Challenge 9 - Phun With Strings

Solution - Challenge Phun With Strings

Lesson 36 - Introduction to Classes and Objects

Challenge - Hero Monster Classes Part 1

Solution - Hero Monster Classes Part 1

Challenge - Hero Monster Classes Part 2

Solution - Challenge Hero Monster Classes Part 2

Lesson 37 - Creating Class Files Creating Cohesive Classes and Code Navigation

Lesson 38 - Understanding Object References and Object Lifetime

Lesson 39 - Understanding the .NET Framework and Compilation

Lesson 40 - Namespaces and Using Directives

Lesson 41 - Creating Class Libraries and Adding References to Assemblies

Lesson 42 - Accessibility Modifiers, Fields and Properties

Lesson 43 - Creating Constructor Methods

Lesson 44 - Naming Conventions for Identifiers

Lesson 45 - Static vs Instance Members

Challenge 10 - Challenge Simple Darts

Solution - Challenge Simple Darts

Lesson 46 - Working with the List Collection

Lesson 47 - Object Initializers

Lesson 48 - Collection Initializers

Lesson 49 - Working with the Dictionary Collection

Lesson 50 - Looping with the foreach Iteration Statement

Lesson 51 - Implicitly-Typed Variables with the var Keyword

Challenge 11 - Challenge Student Courses

Solution - Challenge Student Courses

Mega Challenge War

Solution - Mega Challenge War

Lesson 52 - Creating GUIDs

Lesson 53 - Working with Enumerations

Lesson 54 - Understanding the switch() Statement

Lesson 55 - First Pass at the Separation of Concerns Principle

Lesson 56 - Understanding Exception Handling

Lesson 57 - Understanding Global Exception Handling

Lesson 58 - Understanding Custom Exceptions

Lesson 59 - Creating a Database in Visual Studio

Lesson 60 - Creating an Entity Data Model

Lesson 61 - Displaying the DbSet Result in an ASP.NET GridView

Lesson 62 - Implementing a Button Command in a GridView

Lesson 63 - Using a Tools-Centric Approach to Building a Database Application

Lesson 64 - Using a Maintenance-Driven Approach to Building a Database Application

Lesson 65 - Creating a New Instance of an Entity and Persisting it to the Database

Lesson 66 - Package Management with NuGet

Lesson 67 - NuGet No-Commit Workflow

Lesson 68 - Introduction the Twitter Bootstrap CSS Framework

Lesson 69 - Mapping Enum Types to Entity Properties in the Framework Designer

Lesson 70 - Deploying the App to Microsoft Azure Web Services Web Apps

Papa Bob's Mega Challenge

Papa Bob's Mega Solution Part 1 - Setting up the Solution

Papa Bob's Mega Solution Part 2 - Adding an Order to the Database

Papa Bob's Mega Solution Part 3 - Passing an Order from the Presentation Layer

Papa Bob's Mega Solution Part 4 - Creating the Order Form

Papa Bob's Mega Solution Part 5 - Adding Enums

Papa Bob's Mega Solution Part 6 - Creating an Order with Validation

Papa Bob's Mega Solution Part 7 - Calculating the Order Price

Papa Bob's Mega Solution Part 8 - Displaying the Price to the User

Papa Bob's Mega Solution Part 9 - Creating the Order Management Page


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