Quick Learn – Formatting Decimal and Whole Numbers

This post will show how to use some simple logic and formatting to display only two decimal places with decimal numbers, and no decimal places with whole numbers.

I recently updated a game I wrote in Windows PowerShell called, “The 1 to 100 Game.” In this game, a person tries to guess a number between 1 and 100 that has been chosen by the computer (or rather, the advanced function). The computer will offer hints, as to whether the number it has chosen, is higher or lower than what was last guessed by the person playing the game. This person continues to guess until they correctly match the number. You can find the advanced function on the Microsoft TechNet Gallery here: http://gallery.technet.microsoft.com/The-1-to-100-Game-5288e279. While it’s not my most popular advanced function, I enjoyed the project, and especially when I shared it with my son as the 1 to 100 Game is one of the many games we play during our longer car rides. Oh, and if you’re looking for an example of nested do-while language constructs, then look no further – it’s up to three now.

During the rewrite to version 2.0, I decided to add something new. The game records the number of attempts it takes to guess the correct number, and how many games you’ve played. With that type of information, it can easily calculate the average number of attempts per game. This won’t always be a whole number and so I needed a way to only use two decimal places when decimal numbers were returned, and to use no decimal places when whole numbers were returned.

We can format our decimal numbers to only use two decimal places by using the -f Format operator. In the example below, we take a number that has four decimal places and specify that it is formatted to only use two decimal places.

PS C:\> $x = 100.9851
PS C:\> $x
100.9851
PS C:\> '{0:N2}' -f $x
100.99 #We want this, and notice the rounding!

In the next example, we have a whole number. If we use the -f Format operator on this number it will also show two decimal places. This isn’t what we want – we want to leave whole numbers the way they are and not add any decimal places.

PS C:\> $x = 150
PS C:\> $x
150
PS C:\> '{0:N2}' -f $x
150.00 #We don't want this!

Formatting decimal numbers, and leaving whole numbers alone, is going to require some conditional logic (If-Else statement) along with modulus division. Modulus division returns the remainder of a division operation. Here are some examples using the division operator (/) and the modulus operator (%).

PS C:\> 10 / 2
5
PS C:\> 10 % 2
0
PS C:\> 10 / 3
3.33333333333333
PS C:\> 10 % 3
1
PS C:\> 10 / 7
1.42857142857143
PS C:\> 10 % 7
3

When zero is returned from a modulus division operation, it means that the division operation did not result in a remainder. This is a great way to handle whether or not a number should or should not be formatted. In the example below, the modulus division operation on line 3 returns zero. Since zero is equal (-eq) to zero, then $a is divided by $b on line 4.

$a = 10
$b = 2
If ($a % $b -eq 0) {
    $a / $b
} Else {
    '{0:N2}' -f ($a / $b)
}
5

In this example, the modulus division operation does not return zero. Therefore, the else statement is called on line 5. On line 6, $a is divided by $b and then formatted to two decimal places. The parenthesis around ($a / $b)  indicates to PowerShell to divide first, and then do the formatting.

$a = 10
$b = 3
If ($a % $b -eq 0) {
    $a / $b
} Else {
    '{0:N2}' -f ($a / $b)
}
3.33

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