Introduction to Conditionals

Transcription

1 Introduction to Conditionals Conditional Statements Conditional statements are a key to programming and give us control over basic direction following and reasoning that the computer does. Conditional statements allow us to present and help the computer choose whether or not to run a set of code. There are three types or sets of conditional statements we can use to make choices. These are if, if/else, and if/else if statements. There are scenarios where each of these would be useful. Let s take a look at some scenarios using the ninches variable from the Introduction to Programming document and a new variable we can change in the Inspector. I have edited my code to include a [SerializedField] integer named ninspectorentry, set it to 0, and cleaned up the Start method: Before we even run the program, you can see the addition of this new field in the inspector under our FollowAlong(Script) entry: Programming - Conditionals Pg. 1

2 This will allow us to change this integer to see how our different conditional statements react. Let s try a basic if statement to see if/else ninches and ninspectorentry are equal to each other. The set up for an if/else statement is as follows: Declaration Condition Definition if ( ) { code } else { code } The condition/question inside the parenthesis must equal true/yes in order for the code in the if s curly brackets to run. Otherwise, the code in the else s curly brackets will run. We want to use the if/else combo if there are two outcomes that we need a reaction to. Much like a yes or no question on a quiz that then asks you to explain why or why not. So we are asking the question: Are ninches and ninspectorentry equal? Which would look like this in our code: I placed basic print() calls so that we can see in the console if the answer to our question was true or false. Remember that ninches is set to 64 at the beginning of Start() and ninspectorentry is set to 0, and this should tell us they are not equal when we run it. Programming - Conditionals Pg. 2

3 Great! That works as expected. But what if we wanted to change the ninspectorentry to 64 to see if the if statement also works? If I change the ninspectorentry on the Inspector to 64 while the game is running nothing happens: In order to get the if statement to accept changes to our Inspector Entry, we have to move that entire chunk of code from inside the Start() method and into the Update() method like so: Programming - Conditionals Pg. 3

4 CMD + X for Mac :: CTRL + X for Windows will cut highlighted text out of one area. CMD + V for Mac :: CTRL + V for Windows will paste cut or copied text to another area. After we have saved our code and run it, you can see that now there are numerous prints of the NOT true string. Programming - Conditionals Pg. 4

5 If we swap to our Inspector and change our Inspector Entry to 64 and then switch back to our console, it will then start reprinting that the two integers are equal. The major difference is that the parameters are asking a question that must turn out to be true. This means there are ways to determine if values are not equal, less than or greater than each other. Let s change our conditional operator from == to > so we are asking the question: Is ninches greater than ninspectorentry? Which would look like this in our code: Programming - Conditionals Pg. 5

6 When we start our program again, our ifcondition is true until we change our Inspector Entry to something greater than 64. One thing to note about using conditions is that the computer cannot compare values of different data types. The adage It s like comparing apples to oranges! is literal here. We cannot compare something such as: if( two == 2 ) // if two is equal to 2 as we are comparing a string to an integer, nor could we compare something like: if( true!= false ) // if true doesn t equal false as in this case, we are comparing the Boolean value true to a string that just happens to be the opposite Boolean value. Programming - Conditionals Pg. 6

7 List of Conditional Operators Here is a list of some of the available conditional operators that you can use to create boolean values in an if/else if conditional statement. You can use the result in an if- statement directly, or store the result in a variable. In this list, a and b can be variables or values of almost any type. Normally they would be numbers. The values of abool and bbool must be boolean types, those with a true or false value. a == b equal a!= b not- equal a > b greater- than a >= b greater- than- or- equal a < b less- than a <= b less- than- or- equal abool bbool logical- or abool && bbool logical- and Remember that == is very different from the assignment operator =, and that confusing the two is a common source of errors. Programming - Conditionals Pg. 7

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