Learn to execute Python statement(s) as long as a condition is True
with the help of python while
loop.
1. The while
Loop
- A
while
loop executes a given set of statements in loop, as long as a given conditional expression isTrue
. - As soon as, the conditional expression becomes
False
, thewhile
loop ends.
We should use the while
loop when we do not know the number of iterations beforehand.
Example: Print numbers from 1 to 5 using while loop
In the given example, the value of n
could be anything. Here it is 5.
i = 1 n = 5 while i <= n: print(i) i += 1
Program output.
1 2 3 4 5
In above Python program, the local variable i
store the current number. We initialize i
with initial value 1.
The program prints the value of i
by 1. After program prints i
value to 5, the next time we increment the i
to 6.
At this time, the condition 'i <= 5'
becomes False
and the while
loop exit.
Do not forget to increment the value of
'i'
, elsewhile
loop will never exit. Such loops are called the infinite loops.
Also, be very careful about the code indentation because Python uses indentation for defining the scope of the code blocks.
2. Python while
Loop with 'else'
Statement
The else
statement, in a while
loop, acts very similar to if...else statements. The else
statement executes when the conditional expression in while
loop becomes False.
i = 1 while i <= 5: print(i) i += 1 else: print('The while loop ends')
Program output.
1 2 3 4 5 The while loop ends
3. Python while
Loop with 'break'
Statement
The break
statement helps in exiting the loop even when the conditional expression is True
. When the break
statement is executed, program execution jumps to the next statement immidiately after the while
loop.
i = 1 while i <= 5: print(i) if i == 3: break i += 1 print("Statement after while loop")
Program output.
1 2 3 Statement after while loop
4. Python while
Loop with 'continue'
Statement
The continue
statement helps to exit the current iteration in the loop and start a new iteration from the start of the loop.
When the continue
statement is executed, program execution jumps to the start of the while
loop.
In this Python program, we are printing the value of 'i'
only when it is odd number. In case of i
is even number, we skip the current iteration using the continue
statement.
i = 0 while i <= 5: i += 1 if i % 2 == 0: continue print(i) print("Statement after while loop")
Program output.
1 3 5 Statement after while loop
Happy Learning !!
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