Module: (Python) Nested conditional statement. Difficult conditions


Problem

2/14

Difficult conditions

Theory Click to read/hide

Complex Conditions

The previous problem can be solved in a shorter way using complex conditions. 
Let's understand what complex conditions are.

The simplest conditions consist of one relation (greater than, less than, etc.). But sometimes it is necessary to combine simple conditions into more complex ones. For example, it is cold outside and it is raining. Two simple conditions (it's cold outside), (it's raining outside) are connected here by the copula I.
 
COMPLEX CONDITION - consists of two or more simple relations (conditions) that are combined using logical operations :
  AND - logical multiplication - written in Python as and, < br />   OR - logical addition - written in Python as or,
  NOT - logical negation - in Python written as not.

Operation AND - requires simultaneous fulfillment of two conditions:
  condition 1 and condition 2   - will evaluate to true only if both simple conditions are true at the same time,
moreover, if condition 1 is false, then condition 2 will not be checked

The operation OR - requires at least one of the conditions
  condition 1 or  condition 2   - will evaluate to false only if both simple conditions are false at the same time,
moreover, if condition 1 is true, then condition 2 will not be checked

Operation NOT 
 not condition 1 - will evaluate to false if condition 1 is true and vice versa
For example, the following two conditions are equivalent:   A>B     and    not (A<=B)

 

Priority of execution of logical operations and relations
  1. Operations in brackets
  2. NOT operation
  3. Logical relationships >, <, >=, <=, ==, !=
  4. And operation
  5. OR operation
Parentheses are used to change the order of actions.

 
Boolean variables
In many programming languages, it is possible to use variables that store boolean values ​​("true"/"false"). In Python, such variables can take the values ​​True (true) or False (false). For example, the program   
a=True
b=False
print(a or b)
Displays True.
Boolean variables are of type bool, named after the English mathematician George Boole, the creator of the algebra of logic.

 
 

Problem

In the previous problem we considered, it is necessary to check the condition in which the number must be greater than or equal to 20 and less than or equal to 40. 
You can shorten the previous task using complex conditions.

In the 2nd line of the program, instead of the underscore (_), put the desired logical connective.

time 1000 ms
memory 256 Mb
Rules for program design and list of errors in automatic problem checking

Teacher commentary

Insert the missing code snippets
Python
1 
n = int(input())
2
3 
      print("YES")
4 
else:
5 
      print ("NO")

     

Program check result

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