All the IPython Notebooks in Python Flow Control Statements lecture series by Dr. Milaan Parmar are available @ GitHub
if statement¶We can have a nested-if-else or nested-if-elif-else statement inside another if-else statement. This is called nesting in computer programming. The nested if statements is useful when we want to make a series of decisions.
Any number of these statements can be nested inside one another. Indentation is the only way to figure out the level of nesting. They can get confusing, so they must be avoided unless necessary.
We can use nested if statements for situations where we want to check for a secondary condition if the first condition executes as True.
if conditon_outer:
if condition_inner:
statement of nested if
else:
statement of nested if else:
statement ot outer if
else:
Outer else
statement outside if block
if expression1:
statement(s)
if expression2:
statement(s)
elif expression3:
statement(s)
elif expression4:
statement(s)
else:
statement(s)
else:
statement(s)
# Example 1:
a=10
if a>=20: # Condition FALSE
print ("Condition is True")
else: # Code will go to ELSE body
if a>=15: # Condition FALSE
print ("Checking second value")
else: # Code will go to ELSE body
print ("All Conditions are false")
All Conditions are false
# Example 2:
x = 10
y = 12
if x > y:
print( "x>y")
elif x < y:
print( "x<y")
if x==10:
print ("x=10")
else:
print ("invalid")
else:
print ("x=y")
x<y x=10
# Example 3:
num1 = 0
if (num1 != 0): # For zero condition is FALSE
if(num1 > 0):
print("num1 is a positive number")
else:
print("num1 is a negative number")
else: # For zero condition is TRUE
print("num1 is neither positive nor negative")
num1 is neither positive nor negative
# Example 4:
'''In this program, we input a number check if the number is
positive or negative or zero and display an appropriate message.
This time we use nested if statement'''
num = float(input("Enter a number: "))
if num >= 0:
if num == 0:
print("Zero")
else:
print("Positive number")
else:
print("Negative number")
Enter a number: 9 Positive number
# Example 5:
def number_arithmetic(num1, num2):
if num1 >= num2:
if num1 == num2:
print(f'{num1} and {num2} are equal')
else:
print(f'{num1} is greater than {num2}')
else:
print(f'{num1} is smaller than {num2}')
number_arithmetic(96, 66)
# Output 96 is greater than 66
number_arithmetic(96, 96)
# Output 56 and 56 are equal
96 is greater than 66 96 and 96 are equal