WhileLoop.md

Loop Statement : While Loop

Introduction

• While loops repeat as long as a certain boolean condition is met.
• The while loop in Python is used to iterate over a block of code as long as the test expression (condition) is true.
• Mostly while loop is used when we want to iterate a dynamical number of times repetition of an object.
• The loop iterates while the condition is true.
• When the condition becomes false, program control passes to the line immediately following the loop.
• Iteration means executing the same block of code over and over, potentially many times.

Syntax:

while [condition]:
           #run this code until while condtion is true

Example:

a=10
while a!=0:
  print(a)
  a-=1

Output:

10
9
8
7
6
5
4
3
2
1

Interruption of Loop Iteration

• In each example you have seen so far, the entire body of the while loop is executed on each iteration.
• Python provides two keywords that terminate a loop iteration prematurely:

1. break
2. continue

1.break

• Immediately terminates a loop entirely.
• Program execution proceeds to the first statement following the loop body.

Example:

n= 5
while n > 0:
   n -= 1
   if n == 2:
      break
   print(n)
print('Loop ended.')

Output:

4
3
Loop ended.

when n becomes 2 the break statement is executed.loop is terminated completely, and program execution jumps to the print() statement on line 7.

2. continue

• Immediately terminates the current loop iteration.
• Execution jumps to the top of the loop, and the controlling expression is re-evaluated to determine whether the loop will execute again or terminate.

Example:

n = 5
while n > 0:
 n -= 1
 if n == 2:
     continue
 print(n)
print('Loop ended.')

Output

4
3
1
0
Loop ended.

when n is 2, the continue statement causes termination of that iteration. Thus, 2 isn’t printed. Execution returns to the top of the loop, the condition is re-evaluated, and it is still true.