Java loops

Question 1

What is the syntax of a basic for loop in Java?

Answer 1

for (initialization; condition; increment/decrement) {
System.out.println(i);

Question 2

What does the following for loop do?

for (int i = 10; i >= 1; i–) {
System.out.print(i + “ “);
}

Answer 2

Counts backward from 10 to 1

Question 3

How would you print all even numbers from 1 to 20 using a for loop?

Answer 3

for (int i = 2; i <= 20; i += 2) {
System.out.println(i);
}

Question 4

How does the initialization section of a for loop work? Can you initialize multiple variables?

Answer 4

initialization can be done only once.
Yes, multiple variables can be initialized.

Question 5

Can a for loop be used without an initialization statement?

Answer 5

initialization can be done before the for loop and syntax for it can be left empty.

Question 6

What will happen if the condition in a for loop is omitted?

Answer 6

If the condition in a for loop is omitted, the loop will continue indefinitely, creating an infinite loop. it will keep iterating until it’s manually terminated (e.g., with a break statement or external interruption).

Question 7

How can you break out of a for loop prematurely?

Answer 7

You can break out of a for loop prematurely using the ‘break’ statement. This causes the loop to terminate immediately, regardless of the loop condition.

Question 8

What is the difference between break and continue in a for loop?

Answer 8

break: Immediately terminates the loop, exiting the loop entirely.

continue: Skips the current iteration of the loop and moves to the next iteration, without terminating the loop.

Question 9

How do you nest two for loops to create a multiplication table (from 1 to 5)?

Answer 9

for (int i = 1; i <= 5; i++) {
for (int j = 1; j <= 5; j++) {
System.out.print(i * j + “ “);
}
System.out.println();
}

Question 10

How would you sum all numbers from 1 to 100 using a for loop?

Answer 10

int sum = 0;
for (int i = 1; i <= 100; i++) {
sum += i;
}
System.out.println(sum);

Question 11

How can a for loop iterate over an array in Java?

Answer 11

int[] arr = {10, 20, 30, 40};
for (int i = 0; i < arr.length; i++) {
System.out.println(arr[i]);
}

Question 12

How would you implement an enhanced for loop to iterate over an array?

Answer 12

int[] numbers = {1, 2, 3, 4};
for (int num : numbers) {
System.out.println(num);
}

Question 13

How does a for loop work with a String to print each character separately?

Answer 13

String word = “Java”;
for (int i = 0; i < word.length(); i++) {
System.out.println(word.charAt(i));
}

Question 14

How would you reverse a string using a for loop in Java?

Answer 14

String word = “Java”;
for (int i = word.length() - 1; i >= 0; i–) {
System.out.print(word.charAt(i));
}

Question 15

How can you create an infinite loop using the for loop?

Answer 15

for(;;){
System.out.println(“infinite loop”);
}

Question 16

What is the difference between a for loop and a while loop?

Answer 16

for loop: Typically used when the number of iterations is known beforehand.
while loop: Used when the number of iterations is not known ahead of time, and the loop continues until a specific condition becomes false.

Question 17

How does a do-while loop work, and how is it different from a while loop?

Answer 17

int i = 0;
do {
System.out.println(i);
i++;
} while (i < 5);

the code inside the ‘do’ block runs at least once even if the condition is false. In the while loop, if the condition is alse, the loop is exited instantly.

Question 18

What is the syntax of a basic while loop in Java?

Answer 18

int i = 0;
while (i < 10) {
System.out.println(i);
i++;
}

Question 19

How do you write a while loop that runs until the user inputs a negative number?

Answer 19

Scanner sc = new Scanner(System.in);
int number;
while ((number = sc.nextInt()) >= 0) {
System.out.println(“You entered: “ + number);
}

Question 20

How can you create an infinite loop using a while loop?

Answer 20

while (true) {
System.out.println(“Infinite Loop”);
}

Question 21

How can you modify a for loop to iterate through only odd numbers between 1 and 20?

Answer 21

for (int i = 1; i <= 20; i += 2) {
System.out.println(i);
}

Question 22

How can you use a for loop to find the factorial of a number (e.g., 5!)?

Answer 22

int factorial = 1;
for (int i = 1; i <= 5; i++) {
factorial = factorial * i;
}
System.out.println(factorial);

Question 23

How would you use a for loop to reverse an array in Java?

Answer 23

int[] arr = {1, 2, 3, 4, 5};
for (int i = arr.length - 1; i >= 0; i–) {
System.out.print(arr[i] + “ “);
}

Question 24

How can you use a for loop to check if a number is prime?

Answer 24

A prime number is only divisible by 1 and itself. You can check this by dividing the number by all numbers from 2 to half of the number.

int number = 29;
boolean isPrime = true;
for (int i = 2; i <= number / 2; i++) {
if (number % i == 0) {
isPrime = false;
break;
}
}
System.out.println(isPrime ? “Prime” : “Not Prime”);

Question 25

What will the following for loop output, and why?

for (int i = 0; i < 10; i++) {
if (i % 2 == 0) {
continue;
}
System.out.print(i + “ “);
}

Answer 25

The continue statement skips the current iteration when i is even. Therefore, only odd numbers will be printed.