Unit 2 Practice: Java Iteration

Name: ____________

Write each solution in Java. Use iteration (for, while, or do-while) as the main approach. Do not use recursion. For each problem, create a public class Main and test your code in main.

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Problem 1. Sum from 1 to N

Write a program that reads an integer n and prints the sum of all integers from 1 to n.

Input

10

Output

55

Requirements

• Use a loop.
• If n is less than 1, print 0.

Problem 2. Count Even Numbers

Write a program that reads two integers start and end, then prints how many even numbers are in that range.

The range includes both start and end.

Input

3 12

Output

5

Explanation

The even numbers are 4, 6, 8, 10, 12.

Requirements

• Use a loop.
• Your program should also work when start is greater than end.

Problem 3. Factorial

Write a program that reads an integer n and prints n!.

n! means:

n * (n - 1) * (n - 2) * ... * 1

Input

5

Output

120

Requirements

• Use a loop.
• Use long for the result.
• If n is 0, the answer is 1.
• Assume 0 <= n <= 20.

Problem 4. Prime Number Check

Write a program that reads an integer n and prints whether it is a prime number.

A prime number is greater than 1 and has only two positive divisors: 1 and itself.

Input

17

Output

prime

Another Input

21

Another Output

not prime

Requirements

• Use a loop to check divisors.
• 1 is not a prime number.
• Try to stop the loop early when you already know the answer.

Problem 5. Print All Prime Numbers in a Range

Write a program that reads two integers start and end, then prints all prime numbers in that range.

The range includes both start and end.

Input

10 30

Output

11 13 17 19 23 29

Requirements

• Use nested loops.
• Your program should also work when start is greater than end.
• Print the prime numbers on one line separated by spaces.

Problem 6. Multiplication Table

Write a program that reads an integer dan and prints its multiplication table from 1 to 9.

Input

7

Output

7 x 1 = 7
7 x 2 = 14
7 x 3 = 21
7 x 4 = 28
7 x 5 = 35
7 x 6 = 42
7 x 7 = 49
7 x 8 = 56
7 x 9 = 63

Requirements

• Use a loop.
• Match the output format exactly.

Problem 7. Sum of Digits

Write a program that reads a positive integer n and prints the sum of its digits.

Input

5079

Output

21

Explanation

5 + 0 + 7 + 9 = 21

Requirements

• Use a while loop.
• Use % and / to separate digits.
• Assume n > 0.

Problem 8. Reverse a Number

Write a program that reads a positive integer n and prints the number with its digits reversed.

Input

12340

Output

4321

Requirements

• Use a loop.
• Use % and / to process digits.
• It is okay if leading zeroes disappear after reversing.

Problem 9. Greatest Common Divisor

Write a program that reads two positive integers a and b, then prints their greatest common divisor.

The greatest common divisor is the largest integer that divides both numbers.

Input

24 36

Output

12

Requirements

• Use a loop.
• You may use either a simple divisor search or the Euclidean algorithm.
• Assume a > 0 and b > 0.

Problem 10. Fibonacci Sequence

Write a program that reads an integer n and prints the first n Fibonacci numbers.

The Fibonacci sequence starts like this:

0 1 1 2 3 5 8 13 ...

Input

8

Output

0 1 1 2 3 5 8 13

Requirements

• Use a loop.
• Assume 1 <= n <= 45.
• Print the numbers on one line separated by spaces.

Problem 11. Star Triangle

Write a program that reads an integer n and prints a left-aligned triangle of stars.

Input

5

Output

*
**
***
****
*****

Requirements

• Use nested loops.
• Assume 1 <= n <= 20.

Problem 12. Number Pyramid

Write a program that reads an integer n and prints a centered number pyramid.

Input

4

Output

   1
  121
 12321
1234321

Requirements

• Use nested loops.
• Use spaces to align the pyramid.
• Assume 1 <= n <= 9.