Logical Operators Part 3

Part of the Fundamentals section of Coddy's C# journey — lesson 24 of 69.

When checking multiple conditions, the computer stops checking as soon as it knows the final answer (This is called short-circuit evaluation).

For example:

int x = 0;
int y = 5;
bool result = x != 0 && y / x > 2;

Here x equals 0, therefore it will not evaluate y / x > 2. If we would reverse the order:

bool result = y / x > 2 && x != 0;

This will result in an error because y will be divided by 0 which is illegal in math.

This technique is used to optimize the evaluation of logical expressions. For example:

int a = 0;
int b = 2;
int c = 3;
int d = 5;
bool result = (a > 0 && b < 2) || (c < -5 && d < 10);

In this example b < 2 and d < 10 will not be evaluated because a > 0 and c < -5 are both false.

Challenge

Beginner

Let's create a program to decide if it's a good day for solar panel energy production

Initialize these variables:

isSunny with the value true
windSpeed with the value 5.4
temperature with the value 23
solarPanelOutput with the value 9
isCloudy with the value false

Create one logical expression that checks ALL of these conditions:

It's sunny
The wind speed is less than 10
The solar panel output is less than 15
The temperature is above 20 OR there are no clouds

Cheat sheet

Short-circuit evaluation means the computer stops checking conditions as soon as it knows the final answer.

With && (AND), if the first condition is false, the second won't be evaluated:

int x = 0;
int y = 5;
bool result = x != 0 && y / x > 2; // y / x > 2 is not evaluated

With || (OR), if the first condition is true, the second won't be evaluated:

bool result = (a > 0 && b < 2) || (c < -5 && d < 10);
// If a > 0 is false, then b < 2 won't be evaluated
// If the first part is false but c < -5 is also false, then d < 10 won't be evaluated

This optimization prevents unnecessary calculations and can avoid errors like division by zero.

Try it yourself

using System;

public class Program {
    public static void Main(string[] args) {
        // Initialize variables
        
        
        // The complete logical expression
        bool result = 
        
        // Don't delete the lines below
        Console.WriteLine("Checking conditions for solar energy production...");
        Console.WriteLine("1. Is it sunny? " + isSunny);
        Console.WriteLine("2. Is wind speed safe? " + (windSpeed < 10));
        Console.WriteLine("3. Can panels produce more? " + (solarPanelOutput < 15));
        Console.WriteLine("4. Is temperature good OR no clouds? " + (temperature > 20 || !isCloudy));
        Console.WriteLine("\nFinal result - Good day for solar energy production: " + result);
    }
}