What's the difference between a procedural program and an object oriented program? [closed]

Answer 1

The difference between the two is subtle but significant.

In a procedural program, modules interact by reading and writing state that is stored in shared data structures.

In an object oriented program, modules in the form of objects interact by sending messages to other objects.

Answer 2

You are correct in your observation that object-oriented programs are based in many ways on the procedural paradigm. You are also correct in that syntactically all that really happens is that you invoke functions. In fact, you could implement many features of object oriented languages using procedural mechanisms (e.g., function pointers in C++). You could thus do an object-oriented design and still implement it in a procedural language (e.g., like old C++ compilers did).

The importance of the object oriented paradigm is not as much in the language mechanism as it is in the thinking and design process. In procedural programming the thinking is about operations and breaking those operations down using other operations, grouping them into modules, etc. This means that the data or state falls into a secondary importance. It is like thinking of mathematical operations.

The object oriented paradigm, on the other hand, says that you need to think of state and operations together as an entity, and then design your program as interactions between entities that exchange state and activate operations.

Answer 3

OO is mostly a mind set. You can program OO in C (if you really want to ... ), and you can perfectly have procedural code in C++/Java; what I mean is, even if you use classes on the surface, it could still be procedural.

The idea behind OO is abstraction of state. Instead of "thinking" in terms of "groupings of data", you "think" in terms of "objects", where an object is an "interface" for "grouping of data and ways to manipulate this data".

It all sounds philosophical, because it is.

There's a lot to say here, and it can't be all said in a small SO post, so I'll leave it here.

UPDATE
As mentioned in Flanagan's answer, OO languages implement constructs that utilize this abstraction.

I mean, you could technically "hack" classes and polymorphism in terms of structs, functions, and function pointers.

Here's an example of OO in C

Answer 4

IMHO, object oriented programming is a concept that exists at a higher level of abstraction than procedural programming. The two are not mutually exclusive in that individual methods in an OO program look pretty much the same as individual functions in a procedural program. This contrasts with, for example, functional programming, which requires a completely different mindset. Furthermore, you can write procedurally in an OO language by making everything static, etc. You can be a human compiler and write effectively OO code in C by using lots of function pointers and struct pointer casting.

OO, then, is more of a design philosophy and world view than something w/ a rigorous definition. It requires that inheritance, polymorphism, etc. be used as major patterns in structuring your code, and that syntax be provided to make these expressible without resorting to low-level tricks. It requires that you think of code that acts on the state of a collection of data as being a property of the data, not a procedure that exists by itself. It is not black and white. Your code can be "more" or "less" OO depending on how heavily you rely on inheritance, polymorphism, classes and the "methods as a property of data" worldview as a means of structuring and explaining/understanding your code.

Answer 5

In a procedural program, you divide a big problem into small problems, and abstract each of these small problems as a procedure. This is called procedural abstraction.

In object oriented programs, you analyse a problem as some objects, and the interaction between objects. This is called object abstraction.