Booleans and Comparison Operators

Word Soup: Conditionals, Booleans, expressions, statements

As you saw in the video there are a bunch of terms that generally are all talking about the same thing.

Boolean, Boolean values, Boolean expressions:

• A Boolean value is simply a computer science-y term that means a true/false value.
• A Boolean expression is a statement that evaluates to a Boolean value (a single true/false).

Condition, Conditionals, Conditional Statements:

• "Conditional" is simply a generic term for code that alters program flow based on true/false values (like an if statement)
• Examples: Condition, Conditionals, Conditional statements, conditional execution

Comparison Operators

A common type of condition to check is a comparison of two values. Here are 6 common comparison operators. Each compares a value on the left with a value on the right and returns a Boolean value -- true or false. Most of these do what you would expect.

Why these symbols: ==, !=, <=, and >=?

1. We use == because the single equal sign = is the assignment operator. We need something different to indicate we want to compare two values instead of assign one to the other.

   Common mistake: writing something like if (age = 18) instead of if (age == 18). We'll make sure we get this down later.

2. We use !=, <=, and >= because they only require ASCII symbols. Historically the mathematical symbols ≠, ≤ and ≥ were hard or impossible to produce on some systems. The ! is universally read as "not".

Reference: Examples

Below are a bunch of examples of how you might see comparisons in code. Review them if you like or continue on and come back if you need reference.

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Compares two values - numbers, strings, or other booleans - and returns true if they are equal, otherwise false.

• "Hello" == "hello" returns false -- because the strings are are capitalized differently.
• "3" == 3 returns true -- because == tries to be forgiving. If it can "coerce" a string into a number it will do so to compare. ¹
• (2+1) == 3 returns true -- because the arithmetic expression evaluates to 3.
• x == 7 returns true -- when the variable x has the value 7.

^1. While it is a useful feature that == will coerce a string into a number, it is considered TRICKY because the string "3" is not the same as the integer 3. There are times when you would believe these are not equal. There is a "strict" equality operator - the "triple equal" === which makes sure that both the type of data and value are equal. So "3" === 3 is false.

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Compares two values - numbers, strings, or other booleans - and returns true if they are not equal, otherwise false.

• "Hello" != "hello" returns true -- because the strings are slightly different.
• "3" != 3 returns false -- because the string 3 can be coerced into a number before comparing with 3. (see notes above about the forgiving ==).
• (2+1) != 3 returns false -- because the arithmetic expression evaluates to 3.
• x != 7 returns true -- when the variable x is any value other than 7.

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Compares two values to see if the number on the left is greater than the number on the right.

• 4 > 3 returns true
• 3 > 7 returns false
• age > 17 returns true -- when the value of the variable "age" is strictly greater than 17, otherwise false.

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Compares two values to see if the number on the left is less than the number on the right.

• 4 < 3 returns false
• 3 < 7 returns true
• age < 17 returns true -- when the value of the variable "age" is strictly less than 17, otherwise false.

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Compares two values to see if the number on the left is less than or equal to the number on the right.

• 3 <= 4 returns true
• 4 <= 3 returns false
• age <= 18 returns true -- when the value of the variable "age" is 18 or less.

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Compares two values to see if the number on the left is greater than or equal to the number on the right.

• 3 >= 4 returns false
• 4 >= 3 returns true
• age >= 18 returns true -- when the value of the variable "age" is 18 or greater.

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