Declarative programming is a programming paradigm … that expresses the logic of a computation without describing its control flow.

Imperative programming is a programming paradigm that uses statements that change a program’s state.

“Programming Paradigm” sounds super pretentious and is definitely a phrase some of my college profs loved. If you’ve had a formal CS education, these definitions may not be that cryptic, but still I find that examples go a long way in helping.

Imperative

There are several sub-paradigms of the imperative programming paradigm, such as the proceduralor the object-oriented programming paradigms.

In the imperative programming paradigm, you describe the algorithm step-by-step, at various degrees of abstraction.

Examples of programming languages which support the procedural paradigm:

• C (and most other legacy languages)
• PHP, mostly
• In some sense, all major languages

Object-Oriented

It typically refers to languages that exhibit a hierarchy of types that inherit both methods and state from base types to derived types, but also includes the unusual prototype-based JavaScript.

Examples of programming languages which support the OO paradigm:

• Java

Declarative

There are several sub-paradigms of the declarative programming paradigm, such as the functional or the logic programming paradigms.

In the declarative programming paradigm, you describe a result or a goal, and you get it via a "black box". The opposite of imperative.

Examples of programming languages which support the declarative programming paradigm:

• yacc
• Treetop
• SQL
• Regular Expressions
• lex
• XSLT
• markup, troff, CSS, VHDL

Functional

Functional programming emphasizes the application of functions without side effects and without mutable state. The declarative systems above exhibit certain aspects of functional programming.

Examples of programming languages which support the declarative functional paradigm:

• Haskell
• OCaml
• Scheme
• Erlang
• F#
• Scala