Chapter 6 :
Informatics practices
Class XI ( As per CBSE Board)
Conditional &
Looping Constructs
New Syllabus 2019-20
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Flowchart
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A flowchart is simply a graphical representation of steps. It shows steps in a sequential order, and is widely used in presenting flow of algorithms, workflow or processes. Typically, flowchart shows the steps as boxes of various kinds, and their order by connecting them with arrows.
Flowchart Symbols
Different flowchart shapes have different conventional meanings. The meanings of some of the more common shapes are as follows:
The terminator symbol represents the starting or ending point of the system.
A box indicates some particular operation.
3. Document
This represents a printout, such as a document or a report.
Flowchart
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4. Decision
A diamond represents a decision or branching point. Lines coming out from the diamond indicates different possible situations, leading to different sub- processes.
5. Data
It represents information entering or leaving the system. An input might be an order from a customer. An output can be a product to be delivered.
6. Flow
Lines represent flow of the sequence and direction of a process.
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Flowchart
Flowchart for addition of two numbers
Control Statements
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Control statements are used to control the flow of execution depending upon the specified condition/logic.
There are three types of control statements.
Decision Making Statement
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Decision making statement used to control the flow of execution of program depending upon condition.
There are three types of decision making statement.
Decision Making Statement
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1. if statements
An if statement is a programming conditional statement that, if proved true, performs a function or displays information.
Decision Making Statement
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1. if statements
Syntax:
if(condition):
statement
[statements]
e.g. noofbooks = 2
if (noofbooks == 2):
print('You have ') print(‘two books’)
print(‘outside of if statement’)
Output
You have two books
Note:To indicate a block of code in Python, you must indent each line of the block by the same amount. In above e.g. both print statements are part of if condition because of both are at same level indented but not the third print statement.
Decision Making Statement
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1. if statements
Using logical operator in if statement
x=1 y=2
if(x==1 and y==2):
print(‘condition matcing the criteria')
Output :-
condition matcing the criteria
a=100
if not(a == 20):
print('a is not equal to 20')
Output :-
a is not equal to 20
Decision Making Statement
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2. if-else Statements
If-else statement executes some code if the test expression is true (nonzero) and some other code if the test expression is false.
Decision Making Statement
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2. if-else Statements
Syntax:
if(condition):
statements
else:
statements
e.g.
a=10
if(a < 100):
print(‘less than 100')
else:
print(‘more than equal 100')
OUTPUT
less than 100
*Write a program in python to check that entered numer is even or odd
Decision Making Statement
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3. Nested if-else statement
The nested if...else statement allows you to check for multiple test expressions and execute different codes for more than two conditions.
Decision Making Statement
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3. Nested if-else statement
Syntax
If (condition):
statements elif (condition):
statements
else:
statements
E.G.
num = float(input("Enter a number: ")) if num >= 0:
if num == 0:
print("Zero") else:
print("Positive number") else:
print("Negative number")
OUTPUT
Enter a number: 5 Positive number
* Write python program to find out largest of 3 numbers.
Iteration Statements (Loops)
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Iteration statements(loop) are used to execute a block
of statements as long as the condition is true.
Loops statements are used when we need to run same code again and again.
Python Iteration (Loops) statements are of three type :-
Iteration Statements (Loops)
condition is checked every time at the beginning of the loop.
Syntax
while (condition):
statement [statements]
e.g.
x = 1
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1. While Loop
It is used to execute a block of statement as long as a given condition is true. And when the condition become false, the control will come out of the loop. The
while (x <= 4): print(x)
x = x + 1
Output
1
2
3
4
Iteration Statements (Loops)
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While Loop continue
While Loop With Else
e.g.
x = 1
while (x < 3):
print('inside while loop value of x is ',x) x = x + 1
else:
print('inside else value of x is ', x)
Output
inside while loop value of x is 1 inside while loop value of x is 2 inside else value of x is 3
*Write a program in python to find out the factorial of a given
number
Iteration Statements (Loops)
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While Loop continue
Infinite While Loop
e.g.
x = 5
while (x == 5): print(‘inside loop')
Output Inside loop Inside loop
…
…
Iteration Statements (Loops)
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2. For Loop
It is used to iterate over items of any sequence, such as a list or a string.
Syntax
for val in sequence:
statements
e.g.
for i in range(3,5): print(i)
Output 3
4
Iteration Statements (Loops)
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2. For Loop continue
Example programs
for i in range(5,3,-1):
print(i)
Output
5
4
range() Function Parameters
start: Starting number of the sequence.
stop: Generate numbers up to, but not including this number. step(Optional): Determines the increment between each numbers in the sequence.
Iteration Statements (Loops)
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2. For Loop continue
For Loop With Else
e.g.
for i in range(1, 4): print(i)
else: # Executed because no break in for print("No Break")
Output
1
2
3
No Break
Iteration Statements (Loops)
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2. For Loop continue
Nested For Loop
e.g.
for i in range(1,3): for j in range(1,11):
k=i*j
print (k, end=' ')
print()
Output
1 2 3 4 5 6 7 8 9 10
2 4 6 8 10 12 14 16 18 20
Iteration Statements (Loops)
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3. Jump Statements
Jump statements are used to transfer the program's control from one location to another. Means these are used to alter the flow of a loop like - to skip a part of a loop or terminate a loop
There are three types of jump statements used in python.
1.break 2.continue 3.pass
Iteration Statements (Loops)
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1.break
it is used to terminate the loop.
e.g.
for val in "string": if val == "i": break
print(val)
print("The end")
Output
s t r
The end
Iteration Statements (Loops)
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2.continue
It is used to skip all the remaining statements in the loop and move controls back to the top of the loop. e.g.
for val in "init": if val == "i":
continue print(val)
print("The end")
Output
n
t
The end
Iteration Statements (Loops)
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3. pass Statement
This statement does nothing. It can be used when a statement is required syntactically but the program requires no action.
Use in loop
while True:
pass # Busy-wait for keyboard interrupt (Ctrl+C)
In function
It makes a controller to pass by without executing any code.
e.g.
def myfun():
pass #if we don’t use pass here then error message will be shown print(‘my program')
OUTPUT
My program
Iteration Statements (Loops)
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3. pass Statement continue
e.g.
for i in 'initial':
if(i == 'i'):
pass else:
print(i)
OUTPUT
n t a L
NOTE : continue forces the loop to start at the next iteration while pass means "there is no code to execute here" and will continue through the remainder or the loop body.