Class 3 - Logical operator, loop

Logical Operators

Logical operators in programming are symbols or keywords that are used to perform logical operations on Boolean values. Boolean values represent true or false, and logical operators allow you to combine or manipulate these values to make decisions in your program.

Logical Operators in JavaScript¶

JavaScript supports three main logical operators: AND (&&), OR (||), and NOT (!).

AND (&&): The AND operator returns true only if both operands are true. Otherwise, it evaluates to false.

var result = true && false; // result is false

OR (||): The OR operator returns true if at least one of the operands is true. It evaluates to false only when both operands are false.

var result = true || false; // result is true

NOT (!): The NOT operator negates the boolean value of its operand. If the operand is true, it becomes false; if it's false, it becomes true.

var result = !true; // result is false

Truth Tables¶

A truth table is a tabular representation of all possible outcomes of a logical expression. Let's create truth tables for the AND, OR, and NOT operators.

AND Truth Table (&&):

Operand 1	Operand 2	Result
true	true	true
true	false	false
false	true	false
false	false	false

OR Truth Table (||):

Operand 1	Operand 2	Result
true	true	true
true	false	true
false	true	true
false	false	false

NOT Truth Table (!):

Operand	Result
true	false
false	true

Practical Use Cases¶

Logical operators are frequently employed in conditional statements and loops, enhancing the decision-making capabilities of programs. Here's a simple example:

var x = 5;
var y = 10;

if (x > 0 && y > 0) {
  console.log("Both x and y are positive.");
} else {
  console.log("At least one of x or y is not positive.");
}

Loop¶

A loop is a programming construct that allows a set of instructions to be repeated multiple times. JavaScript provides several types of loops, but the most common ones are the "for" loop and the "while" loop.

The For Loop in JavaScript:¶

The for loop in JavaScript is a powerful tool that allows you to repeat a set of instructions for a specified number of times. It consists of three optional expressions enclosed in parentheses, followed by a code block. Let's break down the structure of the for loop:

for (expression1; expression2; expression3) {
  // code block to be executed
}

Expression 1:¶

The first expression, expression1, is executed once before the code block. This part of the loop is typically used to initialize a variable. For example:

for (var i = 0; i < 5; i++) {
  // code block to be executed
}

In this example, let i = 0 initializes a variable i to 0 before the loop begins.

Expression 2:¶

The second expression, expression2, defines the condition for executing the code block. The loop will continue running as long as this condition is true. Using the previous example:

for (var i = 0; i < 5; i++) {
  // code block to be executed
}

Here, i < 5 is the condition. The loop will keep running as long as i is less than 5.

Expression 3:¶

The third expression, expression3, is executed after each execution of the code block. It is commonly used for incrementing or decrementing a variable. Continuing with the example:

for (var i = 0; i < 5; i++) {
  // code block to be executed
}

In this case, i++ increments the value of i by 1 after each iteration.

Another example that counts from 1 to 5:

for (var i = 1; i <= 5; i++) {
  console.log(i);
}

Explanation: - var i = 1: This initializes a variable i to 1. - i <= 5: This is the condition that determines whether the loop should continue. It says, "Continue looping as long as i is less than or equal to 5." - i++: This increments the value of i by 1 after each iteration.

The loop prints the values of i to the console from 1 to 5.