Koans/Foundations/AboutAssignmentAndArithmetic.Koans.ps1
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using module PSKoans [Koan(Position = 112)] param() <# Assignment and Arithmetic Operators Just like many other programming languages, PowerShell has special operators designed to work with data. You can use the following command to get a full overview of how operators work: Get-Help about_Operators Loosely, operators fall into a few categories: assignment (=), arithmetic, comparison, redirection, and string operators. In terms of order of operations, arithmetic operators typically execute before comparison operators, followed by string operators, redirection operators, and finally assignment operators execute last. #> Describe 'Assignment Operator' { It 'is used to assign a value to variables' { $ExpectedValue = 1 + 1 $ActualValue = __ $ActualValue | Should -Be $ExpectedValue } It 'is also used to assign a value to properties or elements' { # With arrays, we can assign values directly to indexes $Array = 1, 2, 3 $Array[2] = 5 $Array | Should -Be @(1, 2, 3) # What would change? } It 'can assign values to many variables at once' { $Var1 = $Var2 = $Var3 = $Var4 = __ $Var1 | Should -Be $Var2 $Var2 | Should -Be $Var3 $Var3 | Should -Be $Var4 $Var4 | Should -Be 27 } It 'can assign multiple values to multiple variables' { $Var1, $Var2 = @( "__", "__") $Var1 | Should -Be "Correct" $Var2 | Should -Be "Incorrect" } } Describe 'Arithmetic Operators' { <# These can be used for standard arithmetic with numerical values, as well as some limited usage with arrays and strings that can come in handy. #> Context 'Addition' { It 'is used to add two items together' { 13 + 4 | Should -Be 17 __ + 6 | Should -Be 13 __ | Should -Be (13.7 + 4) } It 'can be used to concatenate strings' { 'My name is ' + 'Jim' | Should -Be 'My name is Jim' __ | Should -Be ('hello' + 'world') } It 'can be used to put arrays together' { <# As we will cover in AboutArrays, this is not so much 'adding' arrays together as it is building a totally new array. It does, however, have its uses. #> $Array = 1, 2, 3, 4, 5 $ExpectedResult = $Array + 7 $Result = @( __ __ 3 __ 5 __ ) $Result | Should -Be $ExpectedResult } It 'behaves according to the type of the left-hand item' { '____' | Should -Be ('10.5' + 11) __ | Should -Be (11 + '12.5') 12.21 + 'FILL_ME_IN' -eq 23.43 | Should -BeTrue # Adding items into typed arrays will also cause the resulting value to be converted [int[]] $Array = @(1, 2, 3, 4, 5) $Array += '17' __ | Should -Be $Array } } Context 'Subtraction' { It 'works similarly to addition' { 12 - 7 | Should -Be 5 __ | Should -Be (11 - 3.5) } It 'cannot be used with strings' { { 'hello' - 'h' } | Should -Throw # However, this work if the string contains a useable number. __ | Should -Be ('12' - '7.5') # In other words, subtraction only operates on numerical values. { @(1, 2) - 1 } | Should -Throw -ExpectedMessage '____' } } Context 'Multiplication' { It 'can be used on both integer and non-integer numerals' { __ | Should -Be (12 * 4) 12.1 * 2 | Should -Be 24.2 } It 'can also be used on strings' { '____' | Should -Be ('A' * 4) '__' * 4 | Should -Be 'NANANANA' } } Context 'Division' { It 'is restricted to numeric use only' { <# As with subtraction, there's no useful meaning of using division on a string so any attempts to do so will throw an error. #> { 'hello!' / 3 } | Should -Throw -ExpectedMessage '____' <# Unlike with other numerical operators, however, division often results in a non-integer (double) value even when both operands are integers. #> 3 / 4 | Should -Be 0.75 __ / 10 -eq 0.5 | Should -BeTrue } } Context 'Modulus' { # Modulus is a bit of an odd one, but common enough in programming. It performs a # division, and then returns the integer value of the remainder. It 'is usually used with integers' { $Remainder = 15 % 7 __ | Should -Be $Remainder } It 'cannot be used on non-numeric values' { $ModulusOnString = { # Some things are better seen when you try them for yourself. $String = 'hello!' $String % 4 } # Only a partially matching phrase from the error message is necessary. $ModulusOnString | Should -Throw -ExpectedMessage '____' $ModulusOnArray = { # If you have trouble, try doing something similar in the console to see what happens. $Array = 1, 10, 20 $Array % 4 } $ModulusOnArray | Should -Throw -ExpectedMessage '____' } } } Describe 'Assignment/Arithmetic Combination Operators' { It 'is a bit unwieldy to assign and increment without combination operators' { $Value = 5 $Value = $Value + 5 __ | Should -Be $Value } It 'is possible to combine assignment and addition' { $Value = 12 $Value += 7 __ | Should -Be $Value } It 'is also possible to combine subtraction with assignment' { $Value -= 3 __ | Should -Be $Value } It 'works the same way with division' { $Value /= 2 $Value | Should -Be 8 } It 'works with multiplication as well' { $Value *= 3 __ | Should -Be $Value } It 'even works with modulus' { # Modulus hasn't been left out, either. $Value = 12 $Value %= 4 __ | Should -Be $Value } } |