To use the if-else statement in Java, you can follow this syntax:

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if (condition) {
    // code to be executed if the condition is true
} else {
    // code to be executed if the condition is false
}

Here's an example to demonstrate its usage:

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int num = 10;

if (num > 0) {
    System.out.println("The number is positive.");
} else {
    System.out.println("The number is not positive.");
}

In this example, if the num variable is greater than 0, it will print "The number is positive." Otherwise, it will print "The number is not positive."

A boolean is a data type in computer programming that can have one of two possible values: true or false. It is often used in conditional statements and loops to control the flow of a program. Here's an example in JavaScript:

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let isStudent = true; // Boolean variable with the value true

if (isStudent) {
  console.log("You are a student!");
} else {
  console.log("You are not a student.");
}

In this example, the boolean variable isStudent is used in an if-else statement to determine whether the person is a student or not. If the value is true, it will print "You are a student!", otherwise it will print "You are not a student."

The else statement is used in programming to specify an alternative set of code to be executed when a particular condition is not met. It is commonly used in conjunction with the if statement.

Here is an example of how to use the else statement in JavaScript:

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let x = 5;

if (x > 10) {
  console.log("x is greater than 10");
} else {
  console.log("x is less than or equal to 10");
}

In this example, the if condition is x > 10. If this condition evaluates to true, the code within the if block will execute, and the output will be "x is greater than 10". However, if the condition is false, the code within the else block will execute, and the output will be "x is less than or equal to 10".

The else statement provides an alternative code path when the initial condition is not satisfied. It can help in controlling the flow of your program based on different conditions.

In programming, the "&&" and "||" symbols are used in conditional statements, such as the "if" statement, to combine multiple conditions.

The "&&" symbol is known as the logical AND operator. It evaluates to true only if both conditions on its left and right are true. Otherwise, it evaluates to false.

For example:

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if (x > 5 && y < 10) {
  // Code block to execute if both conditions are true
}

In the above example, the code block will only execute if the variable "x" is greater than 5 and the variable "y" is less than 10.

On the other hand, the "||" symbol is known as the logical OR operator. It evaluates to true if at least one of the conditions on its left or right is true. It evaluates to false only if both conditions are false.

For example:

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if (x > 5 || y > 10) {
  // Code block to execute if at least one condition is true
}

In the above example, the code block will execute if either the variable "x" is greater than 5 or the variable "y" is greater than 10. It's not necessary for both conditions to be true for the code block to execute.

These logical operators are used to create more complex conditions in programming, allowing you to control the flow of your code based on different combinations of conditions.

In programming, the "or" operator is represented by the double vertical bar symbol ||. It is used to combine two conditions so that if either one is true, the combined condition is also true. Here is an example in JavaScript:

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if (x > 5 || y < 3) {
  // Do something if either x is greater than 5 or y is less than 3.
}

In this example, the code inside the curly braces will execute if either the condition x > 5 or y < 3 is true.

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import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter a string: ");
        String original = input.nextLine().toLowerCase();

        String reverse = "";
        for (int i = original.length() - 1; i >= 0; i--) {
            reverse += original.charAt(i);
        }

        if (original.equals(reverse)) {
            System.out.println(original + " is a palindrome");
        } else {
            System.out.println(original + " is not a palindrome");
        }
    }
}

This code prompts the user to enter a string, converts it to lowercase, and checks if the string is a palindrome or not. If the string is a palindrome, it prints a message indicating that the input string is a palindrome. Otherwise, it prints the message that the input string is not a palindrome. A palindrome is a word, phrase, number, or other sequence of characters that reads the same forward and backward (ignoring spaces, punctuation, and capitalization).

In programming, a boolean is a data type that can only have one of two values: true or false. It is used to represent logical values and is named after the mathematician George Boole who first defined an algebraic system of logic. Boolean values are commonly used in conditional statements and comparisons. Here is an example of a boolean expression in JavaScript:

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let isSheCodesStudent = true;

if (isSheCodesStudent) {
  console.log('Welcome SheCodes student!');
} else {
  console.log('Sorry, you need to enroll in a SheCodes course first.');
}

Python

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word = input("Enter a word: ")
new_word = ""

for i in range(0, len(word), 2):  
    # iterating over the string, starting at 0 with a step of 2

    if i == len(word) - 1: 
        # if the index is at the last character, add it to the new word
        new_word += word[i]
    else:
        # if not, switch the positions of the two letters and add them to the new word
        new_word += word[i + 1] + word[i]

print("Original word:", word)
print("New word with swapped letters:", new_word)

Explanation:

• The user is prompted to input a word and the input is stored in the variable word.
• new_word is initialized as an empty string, which will hold our modified word.
• We iterate over the word string using a for loop that increments by 2. This allows us to access two letter positions at a time.
• If the current index is at the end of the string, we add the last letter to new_word.
• If not, we switch the positions of the two letters by appending the second letter first and the first letter second.
• Finally, we print both the original word and the modified word.

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const firstName = prompt("What is your first name?");
if(firstName !== null && firstName !== ""){
  alert(`Welcome, ${firstName}`);
} else {
  alert("Too bad for you");
}

You can use a conditional statement to evaluate whether a person is above or below 18.

Here's an example code in JavaScript:

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let age = 20;

if (age >= 18) {
  console.log("Above 18");
} else {
  console.log("Below 18");
}

In this example, the if statement checks if the value of the age variable is greater than or equal to 18. If it's true, then the code inside the curly braces following if will run, which in this case is console.log("Above 18").

If the condition in the if statement is not met (i.e. the value of age is less than 18), then the code inside the curly braces following else will run, which in this case is console.log("Below 18").