What is a loop?
Loops are used in programming execute block of code repeatedly.
What is while loop?
The while loop is used to iterate a block of code until a condition is true.
Syntax of while Loop
while (condition ):
How the while Loop works?
The while loop, first test the condition
If the condition is true, it executes the block, it is called iteration
After one iteration, the condition is checked again. This continues until the condition becomes false.
The while loop is determined through indentation.
While the block starts with an indented line of code and the first unindented line of code has marked the end.
Flowchart of while Loop
Flowchart for while loop in Python
Example: While Loop using counter
The loop with counter allows to iterate the loop define numbers of times.
# Program to print numbers up to n
n = int(input("Enter n: "))
# initialize the counter
counter = 1
while counter <= n:
counter += 1 # update the counter
In the above program, the condition counter =1 is True, it enters the while block.
It prints the value counter and increment the counter, and check the condition until it is true and print the counter, once the counter is 6, condition becomes False and the loop is terminated.
Caution with a while loop
In the case counter loops it is important to note that counter variable must to increment or decrement, failing to do so leads to an infinite loop, since condition remains True forever.
While loop with else
While loops can have an optional else block. The else part is executed when the condition evaluates to False.
Here is an example to illustrate this.
number = int(input("Enter number: "))
counter = 1
sum = 0
while counter <= number:
sum = sum + counter
counter = counter + 1
print("The sum is ", sum)
Infinite loop is a loop where condition always remains true. Few examples of infinite loops are:
Sentinel-controlled loops are sometimes called indefinite repetition because it is not known in advance how many times the loop will execute. These kind of loop uses using a sentinel value (also called a flag value) to indicate "end of loop". The break statement is used along with some the condition for example.
counter = 1
while ( True) :
if ( counter == 5):
print("Exiting from the loop")
print("Sentinel-Controlled loops ", counter)