# Introduction to Scientific Computation Using Python

Video 6 : Relational Operators and If construct

## Basic Relational Operators in Python

Operator Name Operation Remark
< Less than a < b Returns True if a is less than b. Else returns False.
<= Less than or Equal to a <= b Returns True if a is less than or equal to b. Else returns False.
> Greater than a > b Returns True if a is greater than b. Else returns False.
>= Greater than or equal to a >= b Returns True if a is greater than or equal to b. Else returns False.
== Equal to a == b Returns True if a is equal to b. Else returns False.
!= Not Equal to a != b Returns True if a is not equal to b. Else returns False.

## Basic Logical Operators in Python

Operator Name Operation Remark
or Boolean Or con1 or con2 Returns True if either con1 or con2 is True. Else returns False.
and Boolean And con1 and con2 Returns True if both con1 and con2 are True. Else returns False.
not Boolean Not not con1 Returns True if con1 is False

## If-else construct

if (condition1):
# statements to execute if the condition1 is true
elif (condition2):
# statements to execute if the condition2 is true
elif (condition3):
# statements to execute if the condition3 is true
...
elif (conditionN):
# statements to execute if the conditionN is true
else:
# statements to execute if all the N conditions fail


### Note

The Tabs here are necessary! The tab indicates that the indended statements are a part of the construct.

## Updated Heron’s Formula

Check if the inputs actually make a valid triangle.

'''
Program to calculate the area of a triangle using Heron's formulae
'''

# Get inputs
a = float(input("Enter the side 'a' of the triangle:"))
b = float(input("Enter the side 'b' of the triangle:"))
c = float(input("Enter the side 'c' of the triangle:"))

if (a <= 0.0 or b <= 0.0 or c <= 0.0):
print("Sides of a triangle can't be zero or negative!")
elif ( c >= a+b or b >= a+c or a >= b+c):
print("The values violate triangle inequality!")
else:
print("All conditions are valid!")
# Calculate the semi-perimeter
s = (a + b + c)*0.5

# Find the Area
Area = (s*(s-a)*(s-b)*(s-c))**0.5

# Print the result
print("The area of the triangle with sides a = {}, b = {}, and c = {} is {}".format(a, b, c, Area))