📓 Booleans, Branching, and Operators

As we learned in Intro, we can use branching to execute different code depending on specific conditions. In this lesson, we'll learn how to create booleans in C#. Then, we'll learn how to use both if/else and switch statements. We'll end this lesson by reviewing the operators we can use within conditionals and other resources for continued learning and exploration.

Booleans

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As we covered in Intro, booleans can hold one of two values: true or false. We can use the C# equality operator == to see if one thing is equal to another. If it is true, C# returns a boolean with a true value. If it isn't, C# will return a false value.

In Intro, we used JavaScript's strict equality operator === to determine whether two things are completely identical, including their types. In C#, we only use two equals signs == to evaluate equality.

Comparison Operators and Booleans

Let's open the C# REPL (with the $ dotnet-script command) and observe several operators that return booleans.

We can compare two strings like this:

> "1" == "1"
true

The same is true for int data types:

> 1 == 1
true

If we compare things that aren't the same, C# will return false:

>  "1" == "2"
false

bool Variables

In C#, we can declare boolean variables with the bool data type:

> bool mathIsWrong = 1 > 2;
> mathIsWrong
false
> bool mathIsRight = 1 < 2;
> mathIsRight
true

Branching

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Next, we'll learn how to write an if/else statement in C#. First, take note that if/else statements are impossible to run in the dotnet-script REPL without changing the standard indentation and spacing; so, we'll review the following examples of branching without running them in the REPL. Later in the pre-work we'll take the time to run and test branching that we add to a console application

Writing an if/else statement is the same in C# and in JavaScript, except for the indentation. Let's write an if/else statement determine whether someone is old enough to see an R-rated film in theaters:

int intUserAge = 16;
if (intUserAge >= 17) 
{
  return "You can see the movie!";
} 
else 
{
  return "I'm sorry, you are too young to see the movie.";
}

Our branching statement evaluates an age saved in intUserAge and then returns a string with a message depending on whether or not they are 17 year old.

As we can see, the main difference between C# and JavaScript is the spacing and indentation, where the curly brackets are always on a new line, as are the if and else statements themselves.

Just like in JavaScript, we can also include an else if statement, as many as we need. Let's update our code to include a special message to 16 year olds letting them know they are almost the right age to be let into a movie that is rated R.

int intUserAge = 16;
if (intUserAge >= 17) 
{
  return "You can see the movie!";
} 
else if (intUserAge == 16)
{
  return "You're almost there! One more year and you'll be 17.";
}
else
{
  return "I'm sorry, you are too young to see the movie.";
}

Switch Statements

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Just like JavaScript, in C# we can use switch statements as an alternative to branching with if/else.

Here's an example of the same branching as above in a switch statement. You can copy/paste the following code directly in the dotnet-script REPL to try it out.

int intUserAge = 16;
switch (intUserAge)
{
  case >= 17:
    return "You can see the movie!";
  case 16:
    return "You're almost there! One more year and you'll be 17.";
  default:
    return "I'm sorry, you are too young to see the movie.";
} 

There's a few things to remember about switch cases:

• The switch statement moves through each case to see if it matches the specified expression, in our case the value of intUserAge.
• If there's a match between the case and the expression, then the code within that case will run. In our example case 16 matches the value of intUserAge, so the REPL will return "You're almost there! One more year and you'll be 17.". Notice that we don't need to include == to indicate that we want intUserAge to be equal to 16.
• The default case is run if there are no matches with the specified expression, in our case the value of intUserAge. Our default case will run if intUserAge is any number below 16.
• Even if we match with a case before our default case, all of the cases thereafter will be run unless we include a return or break statement in the matching case; because of this, it's a best practice to always include a return or break; statement in each case.

Other Operators

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It's worth noting that all of the operators we used in JavaScript, we can also use in C#. Let's review the most commonly used operators now:

Equality

Operator	Definition	Example
==	equal to	1 == 1 is true. 1 == 2 is false.
!=	not equal to	1 != 2 is true. 1 != 1 is false.

Relational

Operator	Definition	Example
>	greater than	2 > 1 is true. 1 > 2 is false.
>=	greater than or equal to	2 >= 2 and 2 >= 1 are both true. 2 >= 3 is false.
<	less than	1 < 2 is true. 2 < 1 is false.
<=	less than or equal to	1 <= 1 and 1 <= 2 are both true. 2 <= 1 is false.

Logical

Operator	Definition	Example
||	The conditional logical "or" operator returns true if either statements is true; the second statement won't be evaluated if the first is true.	The code num < 4 || num > 6 will evaluate as true if num is less than 4 OR if num is greater than 6.
&&	The conditional logical "and" operator returns true if both statements are true.	The code num < 4 && num > 1 will evaluate as true if num is BOTH less than 4 AND greater than 1; num would have to be 2 or 3.
!	The logical negation operator returns false if the result is true.	The code num != 2 will evaluate as true so long as num is not 2.

More Resources

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C# actually has a lot of operators that JavaScript does not. For example, there's also the logical OR | and logical ORX ^ operators that can be used outside of conditional statements. To learn more, start by perusing the Microsoft (MS) Docs on operators and expressions.