Small Basic Small Basic E-Books > Beginning Microsoft Small Basic > 4. Small Basic Program Design, Input Methods

Review and Preview

You should now be fairly comfortable with creating and running simple Small Basic programs. In this class, we continue learning new Small Basic topics to expand our programming knowledge. We'll look at some program design ideas, some mathematical functions and at ways to get input from users of your programs. And, we'll build a savings calculator program.

Program Design

You are about to start developing fairly detailed programs using Small Basic. We will give you programs to build and maybe you will have ideas for your own programs. Either way, it’s fun and exciting to see ideas end up as computer programs. But before starting a program, it’s a good idea to spend a little time thinking about what you are trying to do. This idea of proper program design will save you lots of time and result in a far better program.

Proper program design is not really difficult. The main idea is to create a program that is easy to use, easy to understand, and free of errors. That makes sense, doesn’t it? Spend some time thinking about everything you want your program to do. What information does the program need? What information does the computer determine? Decide what programming steps you need to follow to accomplish desired tasks.

This chapter is adapted from the book BEGINNING Microsoft Small Basic by Philip Conrod and Lou Tylee.

To purchase this book in its entirety, please see the Computer Science For Kids web site.

Make the Small Basic code in your methods readable and easy to understand. This will make the job of making later changes (and you will make changes) much easier. Follow accepted programming rules - you will learn these rules as you learn more about Small Basic. Make sure there are no errors in your program. This may seem like an obvious statement, but many programs are not error-free.

The importance of these few statements about program design might not make a lot of sense right now, but they will. The simple idea is to make a useful, clearly written, error-free program that is easy to use and easy to change. Planning carefully and planning ahead helps you achieve this goal. For each program built in this course, we will attempt to give you some insight into the program design process. We will always try to explain why we do what we do in building a program. And, we will always try to list all the considerations we make.

One other consideration in program design is to always build your program in stages. Don’t try to build your entire Small Basic program and test it all at once. This just compounds the possibility of errors. We suggest always building your program in stages. Write a little code. Test that little bit of code making sure it works correctly. Slowly add more and more code. Run and test each code addition. Continue this approach until your program is complete. You will find that this “go slow” approach to creating a Small Basic program will make your programming task much simpler. Give it a try in programs we build.

Small Basic - The Second Lesson

We covered a lot of Small Basic in the last class. This was necessary to introduce you to many basic concepts so you could write your first program. In this briefer second lesson, we look at some mathematical functions.

Mathematical Functions

In Class 3, we saw the Small Basic arithmetic operators that allow us to perform the basics of addition, subtraction, multiplication and division. Like other computer programming languages, Small Basic also has the capability of doing very power mathematical computations. Small Basic’s built-in mathematical functions (also called methods) are often used in these computations. We used a couple of these functions in the Sub Sandwich program (Math.Floor and Math.Remainder)

We don’t expect you to be a mathematical genius to work through these notes, so we will only look at three mathematical functions. First, just what is a function? A function is a routine that computes some value for you, given some information. The format for using a function is:

FunctionValue = FunctionName(ArgumentList)

FunctionName is the name of the function and ArgumentList is a list of values (inputs, separated by commas) provided to the function so it can do its work. In this assignment statement, FunctionName uses the values in ArgumentList to compute a result and assign that result to the variable we have named FunctionValue.

How do you know what Small Basic mathematical functions exist, what type of information they provide and what the arguments are? Check various Small Basic references and the Microsoft Small Basic website. Or, just type the word Math in the Small Basic code window and the help area will display all the functions:

Then, choose a function name and the help window will tell you how to use it. Here is information on the first function we look at (Abs):

As mentioned, we will look at three mathematical functions here. The methods that support mathematical functions are implemented in the Small Basic class named Math. Hence, to refer to a particular function, you write Math, then a period, then the function name.

The first function we examine is the absolute value function. In math, the absolute value is the positive part of a number. The Small Basic function is:


where argument is number we want the absolute value of. The argument can be either an int or double type and the returned value will be the same type as the argument. Some examples:

Example Result
Math.Abs(7) 7
Math.Abs(-11) 11
Math.Abs(-3.14) 3.14
Math.Abs(72.1) 72.1

Have you ever needed the square root of a number? A square root is a number that when multiplied by itself gives you the original number. For example, the square root of 4 is 2, since 2 times 2 is four. There’s a button on your calculator () that will do this for you. In Small Basic, the square root function is:


where Argument is number we want the square root of. The argument must be a non-negative number. Some examples:

Example Result
Math.SquareRoot(4) 2
Math.SquareRoot(36) 6
Math.SquareRoot(72.1) 8.491

The last function we will use in this class is the exponentiation method. In exponentiation, a number is multiplied times itself a certain number of times. If we multiply a number by itself 4 times, we say we raise that number to the 4th power. The Small Basic function used for exponentiation is:

Math.Power(Argument1, Argument2)

Notice the Power function has two arguments. Argument1 is the number we are multiplying times itself Argument2 times. In other words, this function raises Argument1 to the Argument2 power. Some examples:

Example Result
Math.Power(4, 2) 16
Math.Power(-3, 3) -27
Math.Power(10, 2) 10000

In each example here, the arguments have no decimal parts. We have done this to make the examples clear. You are not limited to such values. It is possible to use this function to compute what happens if you multiply 7.654 times itself 3.16 times!! (The answer is 620.99, by the way.)

For the more mathematically inclined reader, you should know that there are many more Small Basic functions available for your use. You might want to look into using them. There are trigonometric functions and inverse trig functions, functions to convert from radians to degrees and vice versa, functions to find extreme values, functions for rounding, logarithm and inverse logarithm functions and a built-in value for pi. (If none of this means anything to you, don’t worry – we won’t be using them in this class).

Program Input Methods

In the example (Sub Sandwich Program) we built in the last class, we established variable values in code and ran the program to see the results. The results were printed by the Small Basic output method WriteLine. If we want to use different values, we need to change the code and rerun. This is a pain! It would be nice, in such a program, to allow a user to type in values while the program is running and have the computer do the computations based on the inputs. This way no code changes or recompiling would be needed to get a new answer. We need such capabilities in our programs.

The Small Basic language has two general methods that supports typed input. The methods are part of the TextWindow object we have been using. The first input method (ReadNumber) allows reading numeric (integer and floating) inputs. Its usage is:

ReturnedValue = TextWindow.ReadNumber()

where ReturnedValue is the number input by the user.

The other method (Read) returns a line of text (string information) input by the user. Its usage is:

ReturnedValue = TextWindow.Read()

where ReturnedValue is the text input by the user.

With either of these methods, the user types the requested input and presses the <Enter> key to have the computer accept the value.

Input Methods Example

Start Small Basic. Click the New Program button in the toolbar. A blank editor will appear. Immediately save the program as InputExample in a folder of your choice. Type these lines in the editor

  1. TextWindow.WriteLine("What is your age?")
  2. UserAge = TextWindow.ReadNumber()
  3. TextWindow.WriteLine("You input " + UserAge)

In this code, we ask for a user to input their age, then write it in the text window.

Run the program (click the Run button or press <F5>). You should see:

Notice how the prompt appears. Type in a value and press <Enter>. Once the number is input, it is assigned to the variable UserAge and the WriteLine method displays the entered value:

Notice the input value appears on a separate line after the prompting question. Most times, you would like this value to be on the same line as the prompt. This can be done by using a different TextWindow method. The WriteLine method appends a new line character to the output text, hence subsequent information goes to that new line. The Write method does not begin a new line. Modify the first line of code with the shaded changes (change the WriteLine method to Write and add a space after the question mark):

TextWindow.Write("What is your age? ")

Rerun the program. Now when you type your age, it appears next to the prompting question:

Run the program again and try to enter non-numeric characters – you won’t be able to. The ReadNumber method only accepts numeric data (the digits 0 through 9, a leading minus sign, or a single decimal point).

Now, let’s test the Read method (to input a string of text). Add these three lines of code that ask for a user’s name in a manner similar to requesting the age:

  1. TextWindow.Write("What is your name? ")
  2. UserName = TextWindow.Read()
  3. TextWindow.WriteLine("You input " + UserName)

Run the program again. Type your age, press <Enter> and you will see the prompt asking for your name:

Enter a string (any characters at all can be typed) and press <Enter> to see:

It seems the input methods are working just fine. Did you notice how building a program in stages (adding a few lines of code at a time) is good? Always follow such a procedure. Before leaving this example and building another program, let’s take a quick look at one other useful Small Basic concept. In the text window above, it would be nice if there was a blank line between each input request. This just makes your output appear a little cleaner, a quality of a well designed Small Basic program. To insert a blank line in the output, just use a WriteLine method with a blank argument:


Add the shaded line to the current code:

  1. TextWindow.Write("What is your age? ")
  2. UserAge = TextWindow.ReadNumber()
  3. TextWindow.WriteLine("You input " + UserAge)
  4. TextWindow.WriteLine("")
  5. TextWindow.Write("What is your name? ")
  6. UserName = TextWindow.Read()
  7. TextWindow.WriteLine("You input " + UserName)

Run the program again and answer the prompts. Notice the new blank line.

This program has been saved in the InputExample folder in the course programs folder (\BeginSB\BSB Code).

Program – Savings Calculator

In this program, we will build a savings account calculator. We will input how much money we can put into an account each month and the number of months we put money in the account. The program will then compute how much we saved. This program is saved in the Savings folder in the course programs folder (\BeginSB \BSB Code).

Program Design

The steps needed to do this calculation are relatively simple:

  1. Obtain an amount for each month’s deposit.
  2. Obtain a number of months.
  3. Multiply the two input numbers together.
  4. Output the product, the total savings.

We will use the ReadNumber method to get user input. The WriteLine and Write methods will be used to output the savings amount. We’ll throw in an additional step to ask for the user’s name (an example of using the Read method).

Program Development

Start Small Basic. Click the New Program button in the toolbar. A blank editor will appear. Immediately save the program as Savings in a folder of your choice.

First, type the following header information and code that adds a window title:

  1. '
  2. ' Savings Program
  3. ' Beginning Small Basic
  4. '
  5. TextWindow.Title = "Savings Calculator"

We will use four variables in this program: one for the user’s name (YourName), one for the deposit amount (Deposit), one for the number of months (Months) and one for the total amount (Total). Type these lines to initialize the variables:

  1. YourName = ""
  2. Deposit = 0.0
  3. Months = 0
  4. Total = 0.0

Now, we start the code, using the steps outlined under Program Design. At any time, after typing some code, you might like to stop and run just to see if things are going okay. That is always a good approach to take. First, ask the user his/her name using this code:

  1. ' ask user name
  2. TextWindow.Write("Hello, what is your name? ")
  3. YourName = TextWindow.Read()

Next, determine how much will be deposited in the savings account each month:

  1. TextWindow.WriteLine("")
  2. ' get deposit amount
  3. TextWindow.Write("How much will you deposit each month? ")
  4. Deposit = TextWindow.ReadNumber()

Notice the insertion of a blank line before printing the prompt. Finally, obtain the number of months:

  1. TextWindow.WriteLine("")
  2. ' get number of months
  3. TextWindow.Write("For how many months? ")
  4. Months = TextWindow.ReadNumber()

With this information, the total deposit can be computed and displayed using a WriteLine method:

  1. TextWindow.WriteLine("")
  2. ' compute and display total
  3. Total = Deposit * Months
  4. TextWindow.WriteLine(yourName + ", after " + months + " months, you will have $" + total + " in your savings.")
  5. TextWindow.WriteLine("")

Save your program by clicking the Save button.

The finished code in the Small Basic editor should appear as:

  1. '
  2. ' Savings Program
  3. ' Beginning Small Basic
  4. '
  5. TextWindow.Title = "Savings Calculator"
  6. ' initialize variables
  7. YourName = ""
  8. Deposit = 0.0
  9. Months = 0
  10. Total = 0.0
  11. ' ask user name
  12. TextWindow.Write("Hello, what is your name? ")
  13. YourName = TextWindow.Read()
  14. TextWindow.WriteLine("")
  15. ' get deposit amount
  16. TextWindow.Write("How much will you deposit each month? ")
  17. Deposit = TextWindow.ReadNumber()
  18. TextWindow.WriteLine("")
  19. ' get number of months
  20. TextWindow.Write("For how many months? ")
  21. Months = TextWindow.ReadNumber()
  22. TextWindow.WriteLine("")
  23. ' compute and display total
  24. Total = Deposit * Months
  25. TextWindow.WriteLine(yourName + ", after " + months + " months,
  26. you will have $" + total + " in your savings.")
  27. TextWindow.WriteLine("")

Run the Program

Run your program. If the program does not run successfully, try to find out where your errors are using any error messages that may appear. We will cover some possible errors in the next class.

When the program runs successfully, you will see:

Type in your name, a deposit amount and a number of months. Your total will be given to you in a nicely formatted string output. Notice how the name, deposit, months and total are all put together (concatenated) in a single sentence, along with a dollar sign ($). Make sure the answer is correct. Remember, a big step in program design is making sure your program works correctly! If you say you want to save 200 dollars a month for 10 months and your computer program says you will have a million dollars by that time, you should know something is wrong somewhere!

When I tried the program, I got:

Notice if I deposit 403.52 (you don’t, and can’t, enter the dollar sign) for 11 months, the program tells me I will have $4438.72 in my savings account.

This program may not seem all that complicated. And it isn’t. After all, we only multiplied two numbers together. But, the program demonstrates steps that are used in every Small Basic program. Valuable experience has been gained in recognizing how to read input values, do the math to obtain desired results, and output those results to the user.

Other Things to Try

Most savings accounts yield interest, that is the bank actually pays you for letting them use your money. This savings account program has ignored interest. But, it is fairly easy to make the needed modifications to account for interest - the math is just a little more complicated. We will give you the steps, but not show you how, to change your program. Give it a try if you’d like:

  • Define a variable Interest to store the yearly savings interest rate. Interest rates are floating decimal numbers.
  • Add additional statements to allow the user to input an interest rate.
  • Modify the code to use Interest in computing Total. The code for that computation is (get ready - it’s messy looking):

    Total = 1200 * (Deposit * (Math.Power((1 + Interest / 1200), Months) - 1) / Interest)

    Make sure you type this all on one line – as often happens, the word processor has made it look like it is on two. As we said, this is a pretty messy expression, but it’s good practice in using parentheses and a mathematical function (Power). The number ‘1200’ is used here to convert the interest from a yearly value to a monthly value.

Now, run the modified program. Type in values for deposit, months, and interest. Make sure you get reasonable answers. (As a check, if you use a deposit value of 300, a months value of 14, and an interest value of 6.5, the total answer should be $4351.13. Note you’d have $4200 without interest, so this makes sense). Save your program.

I told a little lie, I didn’t get $4351.13 in the above example with interest. I actually got $4351.1272052172923076923076923!!!:

I rounded the answer. In such cases, the number should just be displayed with two numbers after the decimal. It is possible to do this using Small Basic but beyond the scope of our discussion at the moment.


Notice the programs are getting a little more detailed as you learn more Small Basic. In this class, you learned about proper program design, mathematical functions and how to add input capabilities to your Small Basic programs. You built a little savings account program. And, an important concept to remember as you continue through this course is to always try to build your programs a few lines of code at a time. A good mantra is “code a little, test a little.” You will introduce fewer errors in your programs using this approach.

Excerpt © Copyright 2010-2013 By Kidware Software LLC All Rights Reserved. Computer Science For Kids, the Computer Science For Kids logo, and related trade dress are trademarks or registered trademarks of Kidware Software LLC. Philip Conrod & Lou Tylee have co-authored dozens of books and tutorials for beginning Microsoft Basic, Small Basic, Visual Basic, and Visual C# developers of all ages for over 25 years.