These AI Class 9 Notes Chapter 8 Python Conditional and Looping Statements Class 9 AI Notes simplify complex AI concepts for easy understanding.
Class 9 AI Python Conditional and Looping Statements Notes
Introduction Class 9 Notes
- The two fundamental building blocks of Python programming: conditional statements and looping statements. These powerful tools allow your programs to make decisions and repeat actions.
- Conditional statements in Python language decide the direction (Control Flow) of the flow of program execution. They evaluate a condition (often true or false) and execute different code blocks based on the outcome.
- Looping statements are all about repetition. They allow you to execute a block of code multiple times, often iterating through a sequence of data like lists or strings.
Control Structure Class 9 Notes
A control structure is a programming language construct which affects the flow of the execution of program.
Various types of control structure are described below
Sequence Statements
Sequence statements refers to the instructions that are executed in the sequence in which they are written in the program. When a program is run, the CPU begins execution, executes some number of statements and then terminates at the end.
The sequence of statements that the CPU executes is called the program’s path. Many programs have been straight line programs. Straight line programs have sequential flow, i.e. they take the same path every time they are run.
For example,
Output
A program which adds two integers
Enter first integer : 5
Enter second integer: 11
Sum is: 16
Selection Statements
These statements allow a program to execute a statement or a set of statements depending upon a given condition.
These statements are also called conditional statements or decision statements. A selection statement is a control statement that allows choosing statement two or more execution paths in a program. Selection statements alter the sequential flow of instructions in a program. This is done using selection statements.
Python provides three types of selectors are described below
1. if statement
The simplest and most common selection structure is the if statement. The if statement allows branch depending upon the value or state of variables. If the condition evaluates true, an action is followed otherwise, the action is ignored.
Syntax
In the above example, the conditional statement under if( ) will be always evaluated as True because the value of x will become 4 before the comparison thus the expression (4>3) yields a True value letting the statement under if () to execute, i.e the output of the above code would be “x is greater”.
Following flowchart illustrated if statement:
2. if-else statement
This statement also tests a conditional expression. If the condition is True, the entire block of statements following the if will be executed.
Otherwise, the entire block of statements following the else will be executed.
Syntax
Following flowchart illustrates if-else statement:
e.g.
x=0
y=3
x=x+y
if (x>y):
print(“x is greater”)
else:
print(“we are in else part because x is not greater”)
If the conditional statement under if( ) is evaluated to be True, then the statements under if( ) block will be executed otherwise the statements under else block will be executed. In an if-else statement, either if block or else block executes, never both.
The above code, produces an output as “we are in else part because x is not greater”. Because the conditional statement under if( ) evaluates as False $x$ is not greater than y, it is same as that of y.
e.g.
if (a==b) :
c=a
In above case, the if will stop and the statements following this line will not be considered a part of if, these statements will be executed irrespective of whether the condition a==b is False or True.
3. if-elif-else statement
Sometimes, we need to execute different statement to perform in different conditions. It requires the evaluation of several conditions.
First of all, the first condition is evaluated, if it is true then respective statements are processed. Otherwise, the next condition is evaluated to process another say of statements. This process is continued for several times.
Expression is tested from the top towards the downside. As soon as the true condition is found, the associated set of statement is executed.
Following flowchart illustrates if-elif-else statement
e.g.
4. Nested if statement
Nested means if statements or if-else statements are placed in the statement block of if statement or else statement.
Syntax
The nested if can have one of the following four forms:
(i) if nested inside both, if part and else part
(ii) if nested inside if part
(iii) if nested inside else part
(iv) One if inside another if statements
range( ) Function Class 9 Notes
The range( ) function is used to generate a sequence of numbers overtime. At its simplest, it accepts an integer and returns a range object (a type of iterable).
The range ( ) function has two sets of parameters, as follows
range (stop)
stop number of integers to generate, starting from zero.
range ([start,] stop [,step])
- start starting number of the sequence.
- stop generate numbers upto, but not including this number.
- step difference between each number in the sequence.
Iterative Statements
Iterative statements or loops enable a program with a cyclic flow of logic. Each statement which is written under the scope of a looping statement gets executed the number of times the iteration/looping continues for.
There are two basic types of looping statements available in Python, they are as follows.
A looping statement enables repetition of tasks under its scope based on a particular condition called as loop-condition.
This loop condition evaluates to either True or False. A loop may be continued till a loop-condition is evaluated as True.
1. while loop
A while loop tests for its ending condition before executing the statements enclosed in the loop body even the first time. So, if the ending condition is met when the while loop beings, the lines of instructions its contains will never be carried out.
Syntax
while(loop-condition):
statement(s)
Following flowchart illustrates while loop
A while continues iteration cycle till its loop condition is evaluated as true. If the loop-condition is false for the first time iteration, then loop will not execute even once.
e.g.
The loop is executed till the x is greater than 0 , as soon x becomes 0 the loop is terminated. We observe that within the scope of the loop the value of $x$ is decremented, so that it approaches to its next previous value. Thus, with each iteration the value of $x$ is added to a variable sum and is decremented by 1.
Let us assume that user inputs a value 4 for $x$ then at
In while loop, the looping condition is evaluated at the beginning of the loop’s scope, i.e. prior to entering into the scope of loop. This type of checking is called “Entry control checking”, if the condition fails this checking, then the entry into the scope of loop will not be allowed. So, while loops are often called as Entry Control Loop.
The while loop can accept expression and not just conditions, the following are all illegal expressions
(i) while (x =x+1)
(ii) while (n–)
(iii) while(count +=i)
When the result of x=x+1, n– or count +=i, evaluates to 0 , then the while condition fails and the loop will exit.
2. for loop
The for statement encloses one or more statements that form the body of the loop, the statements in the loop repeat continuously a certain number of times.
This loop is also an entry control loop, as condition is checked before entering into the scope of the loop.
Syntax
Output
A
B
A
B
A
B
A
B
Difference between ‘for’ loop and ‘while’ loop
| Feature | ‘for’ Loop | ‘while’ Loop |
| Syntax | for (initialization; condition; increment/decrement) | while (condition) |
| Initialization | Initialization is done within the loop structure | Initialization is done before the loop structure |
| Condition | The loop continues iterating until the condition is false | The loop continues iterating until the condition is false |
| Increment/Decrement | Increment or decrement is done within the loop structure | Increment or decrement must be done explicitly within the loop |
| Use Cases | Suitable for iterating over a known range or sequence | Suitable for indefinite iteration or when the number of iterations is unknown |
| Control | More control over the number of iterations | Less control over the number of iterations, but can handle more complex conditions |
| Examples | python for i in range(5): | python while x<5: |
Programs Class 9 Notes
1. For accepting an integer from user and checking if this integer is greater than 10.
Output
Enter a number: 56
Number is 56
56 is greater than 10
2. For adding a number to non-zero real number x.
Output
Please enter a real number: 45.9
Real number is 45.9
The sum is: 145.9
3. For asking a user to answer Yes or No to a question such as “Are you ready to provide your credit card number”?
Output
Are you ready to provide your credit card number
(1 = Yes 0 = No): 0
Your choice: 0
Now we will not continue the processing of transaction
4. To find the number is even or odd with compound statement.
Output
Enter a number:45
The number is 45
Remainder on division by 2 is: 1
The number is an odd number.
5. To accept a positive value from a user and prints the square of the number.
Output
Enter a number : 6
The square of 6 is 36
6. To enter a character and print whether a given character is an alphabet, digit or any character.
Output
Enter a character : a
You entered an alphabet
>>>
Enter a character:2
You entered a digit
7. To print the largest number out of 3 numbers.
Output
Enter first number: 78
Enter second number: 54
Enter third number : 23
i = 78
j = 54
k = 23
The largest number is 78
8. For fibonacci series using while loop.
Output
Enter the limit: 10
0
1
1
2
3
5
8
13
21
Glossary
- Sequence Statements it refers to the instructions that are executed in the sequence in which they are written in the program.
- Selection Statements These statements allow a program to execute a statement or a set of statements depending upon a given condition.
- range( ) Function It is used to generate a sequence of numbers overtime.
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