- Nested loop in Python -

Nested Loop:

 A loop inside a loop. 

 

Have you ever noticed how a queue works in a supermarket?

 The same job like adding the items and generating the bill is repeated till the time there are no more persons left in the queue. 

People stand in a line and when the turn comes their billing is done ..right? 

And how is the billing done? Each item is checked and its cost added. This is done for all items in the shopping basket. (loop)

 Here, generating the bill of a person is implemented as a loop (inner loop), then this loop has to be repeated till the time there are no more persons in the queue(outer loop) ..isn’t it? A nested loop helps us in such scenarios.

 Now let's see how a nested loop works. Here, for each iteration of the outer loop, a complete iteration of the inner loop occurs ie a complete inner loop gets repeated as many times as the outer loop. Let us make it more clear using an example. Suppose you want to generate a multiplication matrix.

● You need a loop that prints the first 10 multiples of a number. (one row) 

● Then, it has to be repeated 10 times(1-10,10 rows)...isn’t it? 

● Here the first loop, which generates the multiples, should be the inner loop, and the one that controls how many times it has to repeat acts as the outer loop.

 Let’s see the program.

Note :

● For each iteration of the outer loop, the inner loop does full iteration. 

● when i =1 , inner loop runs 10 times i.e. j ranges from 1-10 

● The students same happens when i=2,3,... 

● ensures output(i*j) is printed with proper spacing

● The indentation rule applies. More facts on nested loop ● There is no limit on the number of loops inside a loop.

 ● The loops can be either for loop or while loop or a combination of them.

A code to simulate the queue in supermarkets keeping in mind social distancing norms and space constraints. Tokens will be given to persons according to the following pattern.

Another option for implementing the queue can be,

 1 2 3 4 5 

 1 2 3 4

 1 2 3

 1 2

 1

Let us Implement this using a python program.

Python program to simulate supermarket billing process. 

Facts that need to be considered 

1. Add the cost of each item to the final bill. 

2. Once all the items are added, print the bill

3. The above steps have to be repeated for all customers in the queue 

Algorithm 

1. Repeat for all customers 

a. Repeat for all items 

i. Get item cost and qty 

ii. add to total

b. Print final bill

Code: