Logic

We're ready to incorporate logic into our Ruby programs. We'll soon build programs that react dynamically to logical propositions. For now, we'll learn how to construct those propositions and examine the Ruby interpreter's evaluation of them.

Comparison Operators

Ruby provides several operators that compare one object to another. Some are familiar from elementary mathematics. >, <, >=, <=, ==, and != mean what you'd expect: "greater than," "less than," "greater than or equal to," "less than or equal to", "equal to", and "not equal to." Note that ==, not = checks for equality. Recall that = is the assignment operator. Comparison operators allow one to build expressions that the Ruby interpreter can evaluate as logical propositions. The expression generally evaluates to true if the proposition is valid and to false if it is invalid.

Ruby also permits string comparison. "cat" < "dog" returns true because "cat" precedes "dog" alphabetically. One can compare different data types only when checking for equality. "cat" < 4 throws an error. "cat" != false returns true. One can compare arrays only for equality, i.e., one array is neither greater nor less than another: