What is the difference between declarative and procedural programming paradigms?

Solution 1:

Imperative

There are several sub-paradigms of the imperative programming paradigm, such as the procedural or 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

Solution 2:

Declarative programming is where you say what you want without having to say how to do it. With procedural programming, you have to specify exact steps to get the result.

For example, SQL is more declarative than procedural, because the queries don't specify steps to produce the result.

Solution 3:

Let me give you a real-world example: I need a cup of tea.

Procedural:

Go to kitchen
Get sugar, milk, and tea,
Mix them, and heat over the fire till it boils
Put that in a cup and bring it to me

Declarative:

Get me a cup of tea.

In a procedural language, you define the whole process and provide the steps how to do it. You just provide orders and define how the process will be served.

In a declarative language, you just set the command or order, and let it be on the system how to complete that order. You just need your result without digging into how it should be done.