1. control structures in the python.pptx

Python

1. Problem Solving and Python Programming Dr. Srideivanai Nagarajan Associate Professor Control Structures in Python Unit 2

2. Control Structures in Python . A program’s control flow is the order in which the program’s code executes. The control flow of a Python program is regulated by conditional statements, loops and function calls. Python has three types of control structures: Sequential – default mode Selection – used for decision and branching Iteration – used for looping, i.e repeating a piece of code multiple times

3. Selection Control Python Conditions and If statements Python supports the usual logical conditions from mathematics: Equals: a == b Not Equals: a != b Less than: a < b Less than or equal to: a <= b Greater than: a > b Greater than or equal to: a >= b These conditions can be used in several ways, most commonly in "if statements" and loops.

4. Simple if An "if statement" is written by using the if keyword. a = 33 b = 200 if b > a:   print("b is greater than a")   if …. Else a = 33 b = 200 if b > a:   print("b is greater than a") else: print(“a is greater than b”)

5. Indentation Python relies on indentation (whitespace at the beginning of a line) to define scope in the code. Other programming languages often use curly-brackets for this purpose . a = 33 b = 200 if b > a: print("b is greater than a") # you will get an error

6. Elif The   elif  keyword is Python's way of saying "if the previous conditions were not true, then try this condition". a = 33 b = 33 if b > a:   print("b is greater than a") elif  a == b:   print("a and b are equal")  

7. Else The  else keyword catches anything which isn't caught by the preceding conditions. a = 200 b = 33 if b > a:   print("b is greater than a") elif  a == b:   print("a and b are equal") else:   print("a is greater than b")

8. Programs Programs: To check a number is even or odd To check pass or fail Leap year or not Positive or negative Positive, negative or zero

9. # program for even or odd n = int (input("enter a number")) if (n%2==0): print(n, "is even number") else: print(n, "is odd number ") # program for pass or fail mark = int (input("enter the mark")) if (mark >= 50): print(mark, "is pass mark") else: print(mark, "is fail mark ")

10. # + ve - ve or 0 n = int (input("enter a number")) if(n ==0): print(n, " is zero") elif (n > 0): print(n, "is postive ") else: print(n, "is negative")

11. Number is Armstrong or not # armstrong or not a = int (input("enter a number")) s=0 t=a while(a >0): n = a%10 s= s+n *n*n a=a//10 if(s==t): print("the given number is armstrong number", t) else: print("the given number is not armstrong number", t) An Armstrong number of three digits is an integer such that the sum of the cubes of its digits is equal to the number itself. For example, 371 is an Armstrong number since 3**3 + 7**3 + 1**3 = 371 . 153

12. Short Hand If If you have only one statement to execute, you can put it on the same line as the if statement. One line if statement: if a > b: print("a is greater than b")

13. Short Hand If ... Else If you have only one statement to execute, one for if, and one for else, you can put it all on the same line: One line if.. else statement: a = 2 b = 330 print("A") if a > b else print("B") This technique is known as Ternary Operators, or Conditional Expressions. Example One line if else statement, with 3 conditions: a = 330 b = 330 print("A") if a > b else print("=") if a == b else print("B")

14. Logical statements And The and keyword is a logical operator, and is used to combine conditional statements: a = 200 b = 33 c = 500 if a > b and c > a:   print("Both conditions are True") Or The or keyword is a logical operator, and is used to combine conditional statements: a = 200 b = 33 c = 500 if a > b or a > c:   print("At least one of the conditions is True")

15. Logical statements Not The not keyword is a logical operator, and is used to reverse the result of the conditional statement: a = 33 b = 200 if not a > b:   print("a is NOT greater than b")

16. Nested If You can have if statements inside if statements, this is called  nested  if  statements. x = 41 if  x > 10:   print("Above ten,")   if x > 20:     print("and also above 20!")   else:     print("but not above 20.")

17. The pass Statement if statements cannot be empty, but if you for some reason have an if statement with no content, put in the pass statement to avoid getting an error. a = 33 b = 200 if b > a:   pass

18. Python Loops Python has two primitive loop commands: while loops for loops

19. The while Loop With the while loop we can execute a set of statements as long as a condition is true. i = 1 while i < 6:   print(i)   i += 1

20. Program using while loop #print all natural numbers from 1 to n n = int (input("enter a number")) i=1 while(i<=n): print(i) i+=1

21. Sum of numbers from 1 to n #sum of numbers from 1 to n n = int (input("enter a number")) sum =0 i=1 while(i<=n): sum = sum+i i+=1 print("sum value from 1 to",n ," is",sum )

22. Fibonacci series # fibonacci series n= int (input("enter a number")) f1=0 f2=1 i=1 print(f1) print(f2) while(i<=n): f3=f1+f2 print(f3) f1=f2 f2=f3 i=i+1 print("**********")

23. Break and continue statements The break Statement With the break statement we can stop the loop even if the while condition is true: i = 1 while i < 6:   print(i)   if i == 3:     break   i +=  1 The continue Statement With the continue statement we can stop the current iteration, and continue with the next: i = 0 while i < 6:   i += 1   if i == 3:     continue   print(i)

24. The else Statement With the else statement we can run a block of code once when the condition no longer is true: i = 1 while i < 6:   print(i)   i += 1 else:   print("i is no longer less than 6")

25. Programs using while loop Write the following programs using while loop: Print all even numbers from 2 to n Print the sum of digits in a number Find the reverse of a number Find a number is palindrome or not. Print the Fibonacci series Multiplication table

26. Print numbers from 1 to n using while #print numbers from 1 to n using while loop n = int (input("enter a number")) i =1 while(i<=n): print(i) i+=1

27. # print even numbers from 2 to n n = int (input("enter the number")) i=2 while(i<=n): print(i) i+=2

28. Sum of digits of a number #sum of digits n = int (input("enter a number")) n1 = n sum =0 while(n >0): digi = n%10 sum= sum+digi n = n//10 print(" the sum of digits in ",n1, " is ", sum)

29. Reverse of a number #reverse of a number n = int (input("enter a number")) n1 = n rev =0 while(n >0): digi = n%10 rev=rev*10+digi n = n//10 print(" the reverse of ",n1, " is ", rev)

30. Palindrome #palindrome n = int (input("enter a number")) n1 = n rev =0 while(n >0): digi = n%10 rev=rev*10+digi n = n//10 print(" the reverse of ",n1, " is ", rev) if (n1 == rev): print("the number is palindrome") else: print (" the number is not palindrome")

31. Fibonacci series #Fibonacci series n = int (input("enter a number")) num1 = 0 num2 = 1 next_number = num2 count = 1 print(num1) print(num2) while count <= n: print( next_number ) count += 1 num1=num2 num2= next_number

32. Multiplication table # multiplication table n = int (input("enter a number")) i=1 while(i<=12): print( i,"X",n , "=", i*n) i+=1

33. Python For Loops A  for loop is used for iterating over a sequence (that is either a list, a tuple, a dictionary, a set, or a string). This is less like the for keyword in other programming languages, and works more like an iterator method as found in other object-orientated programming languages. With the for loop we can execute a set of statements, once for each item in a list, tuple, set etc . fruits = ["apple", "banana", "cherry"] for x in fruits:   print(x ) The for loop does not require an indexing variable to set beforehand.

34. Looping Through a String Even strings are iteratable objects, they contain a sequence of characters:   for x in "banana":   print(x)

35. The break Statement With the break statement we can stop the loop before it has looped through all the items: Example Exit the loop when x is "banana": fruits = ["apple", "banana", "cherry"] for x in fruits:   print(x)   if x == "banana":     break Example Exit the loop when x is "banana", but this time the break comes before the print: fruits = ["apple", "banana", "cherry"] for x in fruits:   if x == "banana":     break   print(x)

36. The continue Statement With the continue statement we can stop the current iteration of the loop, and continue with the next: Example Do not print banana: fruits = ["apple", "banana", "cherry"] for x in fruits:   if x == "banana":     continue   print(x)

37. The range() Function To loop through a set of code a specified number of times, we can use the range() function, The range() function returns a sequence of numbers, starting from 0 by default, and increments by 1 (by default), and ends at a specified number. Example Using the range() function: for x in range(6):   print(x) Note that range(6) is not the values of 0 to 6, but the values 0 to 5.

38. The range() Function The range() function defaults to 0 as a starting value, however it is possible to specify the starting value by adding a parameter: range(2, 6), which means values from 2 to 6 (but not including 6):   for x in range(2, 6):   print(x) The range() function defaults to increment the sequence by 1, however it is possible to specify the increment value by adding a third parameter: range(2, 30,  3 ): Example Increment the sequence with 3 (default is 1): for x in range(2, 30, 3):   print(x)

39. Else in For Loop The  else keyword in a for loop specifies a block of code to be executed when the loop is finished: Example Print all numbers from 0 to 5, and print a message when the loop has ended: for x in range(6):   print(x) else:   print("Finally finished!") Note:  The else block will NOT be executed if the loop is stopped by a break statement.

40. Else in For Loop Example Break the loop when x is 3, and see what happens with the else block: for x in range(6):   if x == 3: break   print(x) else:   print("Finally finished!")

41. Nested Loops A nested loop is a loop inside a loop. The "inner loop" will be executed one time for each iteration of the "outer loop": adj = ["red", "big", "tasty"] fruits = ["apple", "banana", "cherry"] for x in  adj :   for y in fruits:     print(x, y)

42. The pass Statement for  loops cannot be empty, but if you for some reason have a for loop with no content, put in the pass statement to avoid getting an error. for x in [0, 1, 2]:   pass

43. Programs using for loop 1. Factorial of a number 2. Print multiplication table 3. Print the following pattern * * * * * * 4. Print the following triangle 1 1 2 1 2 3 5. Print all even numbers from 2 to n

44. Factorial of a number n = int (input("enter a number")) fact =1 for i in range(1,n+1): fact = fact*i print("factorial of ", n ," is", fact)

45. Multiplication Table # multiplication table n = int (input("enter a number")) for i in range(1,13): print(i ,"X", n,"= ", i*n) #print(i)

46. Print the following pattern * * * * * * n = int (input("enter a number")) for i in range(1,n+1): for j in range(1, i+1): print ("*", end="") print()

47. Print the following triangle 1 1 2 1 2 3 n = int (input("enter a number")) for i in range(1,n+1): for j in range(1, i+1): print (j, end=" ") print()

48. Print 2 to n n = int (input("enter a number")) for i in range(2,n+1): print(i)

49. Print all even numbers from 2 to n n = int (input("enter a number")) for i in range(2,n+1, 2): print(i)

50. # multiplication table n = int (input("enter a number")) for i in range(1,13): print( i,"X",n , "=", i*n)