Overview of Iterative Functions

Here, we will learn about Iteration.

We'll cover the following

What is Iteration?

Iteration means repeating some steps to achieve the desired outcome. In computer programming, this may involve a mechanism such as a loops.

Iterative code is a block of code that runs in a loop. In other words, the same code is repeated over and over again. The idea is similar to that of recursion.

As we are learning recursion, it is important to have an overview of iteration as well. You might have written simple programs that involve iterating over an array, list, etc.

The concept of Recursion and Iteration is to execute a set of instructions repeatedly.

However, the difference between them is that recursion is simply a method call in which the method being called is the same as the one making the call. Iteration, on the other hand, is when a loop is repeatedly executed until a certain condition is satisfied.

Both recursion and iteration depend on a condition which determines whether to stop execution or continue it.

Format of an Iterative Function

Each iterative function consists of a loop and a conditional statement that determines whether to continue iteration or to stop.

Code flow of an iterative function
Code flow of an iterative function

In the illustration above the dotted line encapsulates the iterative part of the code flow.

Syntax of an Iterative Function

Let’s have a look at how an iterative function is coded in python:

def IterativeFunction() :
  <some local variables if required>
  while <someCondition == TRUE> :
    # Perform a task

Calculating Factorial of a Number

Let’s have a look at the iterative code for calculating factorial of a number. We have already looked at the recursive code in a previous lesson.

 def factorial(targetNumber) :
  index = targetNumber - 1 # set the index to target - 1
  
  while index >= 1 :
    targetNumber = targetNumber * index # multiply targetNumber with one less than itself, i.e, index here
    index -= 1 # reduce index in each iteration
  return targetNumber
# Driver Code
targetNumber = 5
result = factorial(targetNumber)
print("The factorial of " + str(targetNumber) + " is: " + str(result))
Iterative method for calculating factorial of a number

In the Iterative version, we initiate a simple while loop and multiply targetNumber with index in each iteration. index is also reduced by 11 in each iteration. This step is important because other wise our program will be stuck in an infinite loop. The value of index initially is targetNumber - 1. Let’s dry run this code by keeping track of the variables.

In the next lesson, we highlight the major differences between iteration and recursion.