Software Development (MCS-203L) SSUET/QR/114
LAB # 05
ITERATION WITH LOOPS
OBJECTIVE
To get familiar with the different types of loops.
THEORY
A loop can be used to tell a program to execute statements repeatedly. In other word, to
keep a computer doing useful work we need repetition, looping back over the same block
of code again and again.
Type of Loop Statements in Python:
There are 2 types of loop statements in Python language. They are,
1. for
2. while
The for loop:
A Python for loop iterates through each value in a sequence.
Syntax:
In general, the syntax of a for loop is:
for var in sequence:
# Loop body
for loop can be used to simplify the preceding loop:
a) for i in range(endValue):
#Loop body
b) for i in range(initialValue, endValue):
# Loop body
c) for i in range range(initialValue, endValue,k): #k=step value # Loop body
How for loop works:
• A ‘sequence’ holds multiple items of data, stored one after the other. In sequence
introduce strings and data storing techniques.They are sequence-type objects in
Python.
• The variable ‘Var’ takes on each successive value in the sequence, and • The
statements in the body of the loop are executed once for each value.
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• Generate a sequence of numbers using ‘range() function’, range(10) will generate
numbers from 0 to 9 (10 numbers).
Example program for ‘for loop’:
#simple for loop using sequence(string) for letter
in 'Python':
print ('Current Letter :', letter)
Output:
>>> %Run task1.py
Current Letter : P
Current Letter : y
Current Letter : t
Current Letter : h
Current Letter : o Current
Letter : n
Example program for ‘for loop using range( )’:
#Simple for loop using range() for i in
range(1,6):
print("Programming is fun")
Output:
>>> %Run task2.py
Programming is fun
Programming is fun
Programming is fun
Programming is fun
Programming is fun
The while loop:
A while loop executes statements repeatedly as long as a condition remains true.
Syntax:
The syntax of a while loop in Python programming language is:
while loop-continuation-condition:
# Loop body
Statement(s)
How while loop works:
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In while loop first the condition (boolean expression) is tested; if it is false the loop is
finished without executing the statement(s). If the condition is true, then the statements
are executed and the loop executes again and again until the condition is false. Each loop
contains a loop-continuation-condition, a Boolean expression that controls the body’s
execution.
Example program for ‘while loop’:
count = 0 while count < 5:
print("Programming is fun!") count
+= 1
Output:
>>> %Run task3.py
Programming is fun!
Programming is fun!
Programming is fun!
Programming is fun! Programming is fun!
EXERCISE
A.Point out the errors, if any, in the following Python programs.
1. Code
for(;;) {
printf("SSUET") }
Output:
2. Code
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count = 4 while
n < 8
count = count + 3:
print(count)
Output:
3.Code
for v in range(4:8) print(v)
Output:
B.What will be the output of the following programs:
1.Code
i = 1 while i < 10:
if i % 2 == 0:
print(i)
i += 1
Output
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2.Code
i = 1 while
i>0:
print(i)
i = i + 1
Output
1
2
3
4
5
6
7
8
9
.
.
.
.
.
.
infinity
3.Code
for v in range(3, 9, 2):
print(v)
Output
C. Write Python programs for the following:
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1. Write a program that prints the first 10 natural numbers and their sum using ‘for loop’.
Sample output:
The first 10 natural number are :
1 2 3 4 5 6 7 8 9 10
The Sum is : 55
Source Code:
num = 10 if
num < 0:
print("Enter a positive number") else:
sum = 0
# use while loop to iterate until zero
while(num > 0): sum += num num -= 1
print("The sum of the natural numbers is", sum)
Output:
2. Write a program to print the multiplication table of the number entered by the user.
The table should get displayed in the following form.
29 x 1 = 29
29 x 2 = 58
…
29 x 10 = 290
Source Code:
num = int(input("Enter the number: "))
print("Multiplication Table of", num)
for i in range(1, 11):
print(num,"X",i,"=",num * i)
Output:
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3. Write a program that take vowels character in a variable named “vowels” then
print each vowels characters in newline using ‘for loop’.
Source Code:
print("Enter the Character: ") c = input() if
c=='a' or c=='e' or c=='i' or c=='o' or c=='u':
print("\nIt is a Vowel") elif c=='A' or c=='E' or
c=='I' or c=='O' or c=='U':
print("\nIt is a Vowel") else:
print("\nIt is a Consonant") Output:
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