# factors problem

Theresa Marlin

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Posts: 49

posted 7 years ago

I have to do a factors problem:

Write a program that asks the user for an integer and then prints out all its factors. For example, when the user enters 150, the program should print

2, 3, 5, 5

I have

This works for 150, but for a number like 6, it will print 2, 2

I don't know what I'm doing wrong or how to fix it

Thank you!

Write a program that asks the user for an integer and then prints out all its factors. For example, when the user enters 150, the program should print

2, 3, 5, 5

I have

This works for 150, but for a number like 6, it will print 2, 2

I don't know what I'm doing wrong or how to fix it

Thank you!

posted 7 years ago

You have a pretty complex maneuver here...

Basically, you are doing the division to find the "other" divisor (the number that when multiplied to the divisor will yield the orig number) and then checking this "other" divisor to see if it is a divisor. The problem with this is... if the "other" divisor is not a whole number (which for non-factors, it isn't), it will round down. This rounding of the "other" divisor, can cause it to be a valid divisor, when testing it.

Why so complex? Why not test the divisor directly? What's wrong with "number % divisor"?

Henry

Theresa Marlin wrote:

This works for 150, but for a number like 6, it will print 2, 2

I don't know what I'm doing wrong or how to fix it

You have a pretty complex maneuver here...

Basically, you are doing the division to find the "other" divisor (the number that when multiplied to the divisor will yield the orig number) and then checking this "other" divisor to see if it is a divisor. The problem with this is... if the "other" divisor is not a whole number (which for non-factors, it isn't), it will round down. This rounding of the "other" divisor, can cause it to be a valid divisor, when testing it.

Why so complex? Why not test the divisor directly? What's wrong with "number % divisor"?

Henry

Theresa Marlin

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Posts: 49

Campbell Ritchie

Marshal

Posts: 52549

119

posted 7 years ago

You have a test for

I have been teaching undergraduates today and I been telling them off for using the wrong hardware. Then I showed them a pencil and a large eraser, which I think is the equipment you ought to use now, too

Take a number, any number, well 6, take a divisor, any divisor, well 2, and work out what

Now work out what the test after the else if does. What would happen if you simplify that test? Does that second test do anything useful at all?

Lose the bit about

Move the

`number > 0`inside a loop`while (number > 1)`. I hardly think that test is necessary.I have been teaching undergraduates today and I been telling them off for using the wrong hardware. Then I showed them a pencil and a large eraser, which I think is the equipment you ought to use now, too

Take a number, any number, well 6, take a divisor, any divisor, well 2, and work out what

`number % (number / divisor)`will come to. Can you concoct a simpler test which will work?Now work out what the test after the else if does. What would happen if you simplify that test? Does that second test do anything useful at all?

Lose the bit about

`if (number == 1)`Move the

`System.out.println()`call after the end of your loop.
Theresa Marlin

Ranch Hand

Posts: 49