Python Classroom Series – 30/Jul/2020

Conditional Statements

  • If you consider the code
print(1)
print(2)
print(3)
print(4)
print(5)
print(6)
print(7)
print(8)
print(9)
print(10)
  • Python will execute all the lines one after other, now lets try to write a program which will tell if the number is even or odd
  • Lets go back to jarvis
Hi Jarvis
Remember 10 as number
check if 10%2 == 0
if yes show 10 is even
else show 10 is odd
  • Now part of the program still under-construction is as shown below
number = 10 # assignment statement
# Execute next line only when number is even
print("you have chosen an even number")
# Execute next line only when number is odd
print("you have chosen an odd number")
  • To make it right we need to use if statement
if <condition>:
    <block>
  • Now adding if to the program earlier
number = 10 # assignment statement

# Execute next line only when number is even
if number%2 == 0:
    print("you have chosen an even number")

# Execute next line only when number is odd
if number%2 !=0:
    print("you have chosen an odd number")
  • This program looks ok but lets take dynamic input from user, now the program looks like
number = int(input('Enter the number of your choice:  ')) # assignment statement

# Execute next line only when number is even
if number%2 == 0:
    print("you have chosen an even number")

# Execute next line only when number is odd
if number%2 !=0:
    print("you have chosen an odd number")
  • Sample debugging screenshot Preview
  • Will we ever ask questions like
1. are you an engineer?
2. are you not an engineer?
  • Then we have done the same thing in the above program?. To solve this i have if/else statement
if <condition>:
    <true-block>
else:
    <false block>
  • Now our program look like
number = int(input('Enter the number of your choice:  ')) # assignment statement

if number%2 == 0:
    print("you have chosen an even number")
else:
    print("you have chosen an odd number")
  • Debug this program

  • Now lets write a program which calculates average of 3 subjects and gives them grades

average = sub1+sub2+sub3/3

average >= 70 => distinction
average >=60 => first class
average >= 50 => second class
third class
  • Now lets speak with jarvis to make our conversation with python3 simple
Hi jarvis
Take input from user and remember as maths
Take input from user and remember as physics
Take input from user and remember as chemistry
now calculate (maths+physics+chemistry)/3 and remember as average
when average >=70 print distinction
when average >=60 print first class
when average >= 50 print second class
for all other cases print third class

  • So our program will be
maths = int(input("Enter the marks obtained in maths:  "))
physics = int(input("Enter the marks obtained in physics:  "))
chemistry = int(input("Enter the marks obtained in chemistry:  "))
average = (maths+physics+chemistry)/3
if average >= 70:
    print("Distinction")
elif average >= 60:
    print("First class")
elif average >= 50:
    print("Second class")
else:
    print("Third class")
  • Other way of solving this program could be
maths = int(input("Enter the marks obtained in maths:  "))
physics = int(input("Enter the marks obtained in physics:  "))
chemistry = int(input("Enter the marks obtained in chemistry:  "))
average = (maths+physics+chemistry)/3
if average >= 70:
    print("Distinction")
else:
    if average >= 60:
        print("first class")
    else:
        if average>=50:
            print("second class")
        else:
            print("third class")
  • One more of way
maths = int(input("Enter the marks obtained in maths:  "))
physics = int(input("Enter the marks obtained in physics:  "))
chemistry = int(input("Enter the marks obtained in chemistry:  "))
average = (maths+physics+chemistry)/3
if average >= 70:
    print("Distinction")
if 60 <= average < 70:
    print("First class")
if 50 <= average < 60:
    print("second class")
if average < 50:
    print("third class")

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