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Paul is a GIS professor at Vancouver Island U, has a PhD from U of British Columbia, and has taught stats and programming for 15 years.

There are several alternative approaches to the programming process, including procedural programming and functional programming. Learn about the differences between these two approaches.

Approaches to Programming

Programming is a creative process carried out by programmers to instruct a computer on how to complete a task. A program is a set of instructions that tells a computer what to do in order to come up with a solution to a particular problem. There are a number of alternative approaches to the programming process. Two very different approaches are procedural programming and functional programming. Each of these two approaches will be described in some detail.

Procedural Programming

Procedural programming uses a list of instructions to tell the computer what to do step by step. Procedural programming relies on procedures, also known as routines. A procedure contains a series of computational steps to be carried out. Procedural programming is also referred to as imperative or structured programming.

Procedural programming is intuitive in the sense that it is very similar to how you would expect a program to work. If you want a computer to do something, you should provide step-by-step instructions on how to do it. Many of the early programming languages are all procedural. Examples of procedural languages include Fortran, COBOL and C, which have been around since the 1960s and 70s.

A common technique in procedural programming is to repeat a series of steps using iteration. This means you write a series of steps and then tell the program to repeat these steps a certain number of times. This makes it possible to automate repetitive tasks.

Functional Programming

Functional programming is an approach to problem solving that treats every computation as a mathematical function. The outputs of a function rely only on the values that are provided as input to the function and don't depend on a particular series of steps that precede the function.

Functional programming relies heavily on recursion. A recursive function can repeat itself until a particular condition is reached. This is similar to the use of iteration in procedural programming, but now applied to a single function as opposed to a series of steps. Examples of functional programming languages include Erlang, Haskell, Lisp and Scala.

An Example for Comparison

Programming approaches can sound a little bit abstract, so let's look at an example. We'll use the same task and look at how each approach would carry out this task. The task is to calculate Fibonacci numbers. By definition, the first two numbers in a Fibonacci sequence are 0 and 1, and the following numbers are always the sum of the previous two. In mathematical terms, here is what the sequence looks like:

The result is a sequence that looks like this:

0 1 1 2 3 5 8 13 21 34 55 89

Fibonacci numbers are used for a wide range of applications, from describing patterns in nature to the structures of galaxies. So what is the Fibonacci number for n = 100? This is exactly the kind of task you want a computer program to do for you. Don't worry too much about understanding the math - the point is that we want a computer program to do the calculations.

In procedural programming, here is what the code would look like to get the 'nth' number in the Fibonacci sequence:

first = 0 second = 1 for i in range(n-1): fib = first + second first = second second = fib print fib

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This particular example uses the Python programming language, but the code looks similar in another procedural language.

The basic idea behind this code is that you would use a looping structure that iterates a series of steps. With every iteration, you get the next value in the sequence. After one iteration, the value of the variable fib is 1, after the second iteration the value is 2, etc. You repeat this n-1 times, where n represents the number in the sequence you are interested in.

Now let's look at the same task in a functional programming language. Here is what the code would look like:

There are some key differences with the previous example. First, there is no series of small steps to calculate the number, but only a function that does the entire calculation. Notice how the function actually looks very similar to the mathematical description of the Fibonacci sequence.

Second, there is no clearly recognizable loop. The third line of code is a recursive function that keeps repeating itself. Every time the function performs a new calculation, the value of n is reduced. When this reaches the value of 1, the function stops and returns to the value of b, which is the desired number in the sequence.

So what is the 100th number in the sequence? Here is the answer:

354,224,848,179,261,915,075

Both programs produce the same result but use a different approach. In general, procedural programming is more widely used. Functional programming is popular in academia but is also used in other areas that rely heavily on mathematical functions.

Lesson Summary

There are a number of alternative approaches to the programming process. Two very different approaches are procedural programming and functional programming. Procedural programming uses a very detailed list of instructions to tell the computer what to do step by step. This approach uses iteration to repeat a series of steps as often as needed. Functional programming is an approach to problem solving that treats every computation as a mathematical function. This approach uses recursion for a function to repeat itself.

Learning Outcome

After watching this lesson, you should be able to differentiate between procedural programming and functional programming.

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