Chapter 16. PC #8. Sum of Numbers (page 1073)

Write a (Java) method that accepts an integer argument and returns the sum of all the integers from 1 up to the number passed as an argument. For example, if 50 is passed as an argument, the method will return the sum of 1, 2, 3, 4, . . . 50. Use recursion to calculate the sum. Demonstrate the method in a program.

The program should ask the user to enter a number, which is then used to display the sum. if the user enters -1, then exit the program.

Test Case 1

Standard Input

5ENTER 10ENTER -1ENTER 

Please enter a number to calculate the sum or -1 to exit: The sum of first 5 natural numbers is 15. Please enter a number to calculate the sum or -1 to exit: The sum of first 10 natural numbers is 55. Please enter a number to calculate the sum or -1 to exit: 

Test Case 2

Standard Input

-10ENTER 0ENTER 7ENTER -1ENTER 

Please enter a number to calculate the sum or -1 to exit: Invalid number. The entry should be a positive number. Please enter a number to calculate the sum or -1 to exit: Invalid number. The entry should be a positive number. Please enter a number to calculate the sum or -1 to exit: The sum of first 7 natural numbers is 28. Please enter a number to calculate the sum or -1 to exit: