<h5 id="61-introduction">6.1 INTRODUCTION</h5> <ul> <li>The concept of sequence in programming is similar to a bus following a road from one milestone to another to reach the school.</li> <li>Python executes statements in a program one after another from beginning to end, which is known as the flow of control.</li> <li>The flow of control can be implemented using control structures, of which Python supports two types: selection and repetition.</li> <li>An example of a program that executes in sequence is Program 6-1, which takes two input numbers, subtracts the second number from the first, and prints the result.</li> <li>The flow of control in Program 6-1 is determined by the order of the statements, which are executed in an order in which they are written.</li> </ul> <p>======</p> <h5 id="62-selection">6.2 SELECTION</h5> <ul> <li>Decision making in programming is implemented with the help of if. .else statement.</li> <li>The syntax of if statement is: <em>if condition: $\hspace{1cm}$ statement (s)</em></li> <li>The if. .else statement allows two alternative paths and the control condition determines which path gets executed. The syntax for if. .else statement is: <em>if condition: $\hspace{0.5cm}$ statement(s) else: $\hspace{0.5cm}$ statement(s)</em></li> <li>The selection structure using elif is used when multiple conditions need to be checked. The syntax for a selection structure using elif is: <em>if condition: $\hspace{0.5cm}$ statement(s) elif condition: $\hspace{0.5cm}$ statement(s) elif condition: $\hspace{0.5cm}$ statement(s) else: $\hspace{0.5cm}$ statement(s)</em></li> <li>Nested if. .else statements can be used, where an if statement is contained within another if statement.</li> </ul> <p>======</p> <h5 id="63-indentation">6.3 INDENTATION</h5> <ul> <li>In Python, indentation is used to define blocks of code instead of curly brackets in most programming languages.</li> <li>The same level of indentation associates statements into a single block of code and it is a common practice to use a single tab for each level of indentation.</li> <li>The interpreter checks indentation levels very strictly and throws up syntax errors if indentation is not correct.</li> <li>Program 6-4 is an example of an if-else statement where the statements in each block are indented with the same amount of spaces or tabs.</li> <li>The program is used to find the larger of the two pre-specified numbers and the output will be “second number is larger” and “Bye Bye” if the second number is larger than the first number.</li> </ul> <p>======</p> <h5 id="64-repetition">6.4 REPETITION</h5> <ul> <li>Repetition in real life and programming is referred to as iteration.</li> <li>An example of repetition in nature is the life cycle of a butterfly.</li> <li>To print the first five natural numbers, a simple print statement can be used for each number.</li> <li>For printing large sets of natural numbers, looping constructs are more efficient.</li> <li>In Python, the two looping constructs are ‘for’ and ‘while’, controlled by a condition and a control variable.</li> </ul> <p>======</p> <h5 id="641-the-for-loop">6.4.1 The ‘For’ Loop</h5> <ul> <li>The ‘for’ loop in Python is used to iterate over a range of values or a sequence. It is executed for each item in the range, which can be numeric or elements of a data type like a string, list, or tuple.</li> <li>The syntax of the for loop is: <code>for <control-variable> in <sequence/items in range>: <statements inside body of the loop></code>. The loop continues until all items in the range have been traversed.</li> <li>The ‘range()’ function is a built-in function in Python, used to create a list containing a sequence of integers from the given start value to the stop value (excluding stop value), with a difference of the given step value.</li> <li>The range() function parameters are start, stop, and step, all of which must be integers. If start value is not specified, it defaults to 0, and if step is also not specified, it defaults to 1.</li> <li>The range() function is often used in for loops for generating a sequence of numbers, as seen in Program 6-9, which prints the multiples of 10 for numbers in a given range.</li> </ul> <p>======</p> <h5 id="642-the-while-loop">6.4.2 The ‘While’ Loop</h5> <ul> <li>The ‘while’ loop executes a block of code repeatedly as long as the control condition is true.</li> <li>The control condition is tested before any statement inside the loop is executed and after each iteration.</li> <li>If the condition becomes false, the body of the loop is not executed and control is transferred to the statement immediately following the loop.</li> <li>If the condition is initially false, the body is not executed even once.</li> <li>It is important to ensure that the condition eventually becomes false to avoid an infinite loop.</li> </ul> <p>Equation: while test_condition : body of while</p> <p>Programs:</p> <ul> <li>Program 6-10: prints first 5 natural numbers using while loop</li> <li>Program 6-11: finds the factors of a whole number using while loop</li> </ul> <p>======</p> <h5 id="65-break-and-continue-statement">6.5 BREAK AND CONTINUE STATEMENT</h5> <ul> <li>Looping constructs in Python allow for repetition of tasks.</li> <li>The <code>break</code> statement is used to exit a loop completely when a specific condition is met.</li> <li>The <code>continue</code> statement skips certain statements in a loop and moves the execution to the next iteration.</li> <li>These statements provide flexibility to programmers in controlling the flow of execution.</li> <li>Using <code>break</code> and <code>continue</code> can lead to more efficient and well-structured code in specific situations.</li> </ul> <p>======</p> <h5 id="651-break-statement">6.5.1 Break Statement</h5> <ul> <li>The <code>break</code> statement is used in loops to terminate the loop and resume execution of the statement following the loop.</li> <li>In Program 6-12, the <code>break</code> statement is used to terminate the <code>for</code> loop when the value of <code>num</code> becomes 8, resulting in the output “Encountered break!! Out of loop”.</li> <li>In Program 6-13, the <code>break</code> statement is used to stop taking further input from the user and display the sum when the user enters a negative number, resulting in the output “Sum = 12”.</li> <li>In Program 6-14, the <code>break</code> statement is used to terminate the loop when the number is not prime, resulting in the output “2020 is not a prime number” and “22 is not a prime number”.</li> <li>The <code>break</code> statement can also be used in other types of loops, such as <code>while</code> loops, to achieve similar functionality.</li> </ul> <p>======</p> <h5 id="652-continue-statement">6.5.2 Continue Statement</h5> <ul> <li>The <code>continue</code> statement in Python skips the remaining statements inside the body of the loop for the current iteration and jumps to the beginning of the loop for the next iteration.</li> <li>If the loop’s condition is still true, the loop is entered again; otherwise, the control is transferred to the statement immediately following the loop.</li> <li>The <code>continue</code> statement is useful when certain conditions do not require the execution of the remaining statements in the loop for the current iteration.</li> <li>The flowchart of the <code>continue</code> statement is shown in Figure 6.7, which depicts the control jumping to the beginning of the loop after the <code>continue</code> statement is executed.</li> <li>Program 6-15 demonstrates the use of the <code>continue</code> statement, which prints the values from 0 to 6 except for the value 3. The <code>continue</code> statement is executed when the value of <code>num</code> is 3, causing the loop to skip the print statement and continue to the next iteration.</li> </ul> <p>======</p> <h5 id="66-nested-loops">6.6 NESTED LOOPS</h5> <ul> <li>Nested loops are loops that contain another loop inside them.</li> <li>The number of loops that can be nested and the levels of nesting are not restricted in Python.</li> <li>Any type of loop (for/while) can be nested within another loop (for/while).</li> <li>Nested loops are used to solve problems that require multiple levels of iteration, such as generating patterns or finding prime numbers in a given range.</li> <li>In the given examples, nested loops are used to generate patterns, find prime numbers, and calculate the factorial of a given number.</li> </ul> <p>======</p>