Test if input number is divisible by 3.

I want to write a program to request a number from the user, and do one of two things:

• If the number is divisible by three, output that it is divisible by 3 and state the quotient.
• If the number is NOT divisible by three, state this, and report back the quotient and remainder.

[Chunru]

doc input

doc mod

[Walter Roberson]

And watch out for the user entering things that are not numeric scalars.

[Bozza]

I'm very new to MATLAB, so could you please explain how to use the doc input and doc mod functions?

[Chunru]

In matlab command window, key in "doc input" or "doc mod" to see the detaild documentation and examples.

[Bozza]

I have done this so far, just can't seem to find how to display the things I want it to:

prompt = "Input a number:"
x = input(prompt)
%check x is whole positive number
if mod(x,1) == 0
    disp('Your number is valid.')
elseif mod(x,1) ~= 0
    disp('Your number is not valid')
%test if x is divisible by 3
divide=x/3
%mod function to find the remainder
remainder = mod(x,3)
%output
if ; disp('Your number is divisible by three, this many times: .')
elseif disp('Your number does not divide equally into 3, it can divide into three this many times: , with remainder: ')

[Walter Roberson]

mod(x,1) == 0

That will calculate and display a result, but will not use that result to make any decision.

if ; disp('Your number is divisible by three, this many times: .')

You need to give a condition after the if

If remainder is what?

    disp('Your number is divisible by three, this many times: .')

I recommend that you investigate fprintf(()

[Bozza]

I have fixed a few things, however, I can't seem to get fprintf(() to work.

prompt = "Input a number:";
x = input(prompt);
%check x is whole positive number
y=mod(x,1);
if y == 0;
    disp('Your number is valid.');
elseif y ~= 0;
    disp('Your number is not valid');
    %I want to make it so that if this elseif is true, it asks the question
    %again
end
%test if x is divisible by 3
divide=x/3
%mod function to find the remainder
remainder = mod(x,3)
%output
if y == 0 fprintf('Your number is divisible by three, this many times: %d\n', divide && remainder);
elseif y ~= 0 fprintf('Your number does not divide equally into 3, it can divide into three this many times: %d\n', divide, 'with remainder: %d\n', remainder);
end

[Rik]

If you want to repeat something an unknown number of times, you may want to consider a while loop.

Also, if you want something to happen in your else, you don't need to use elseif. In your code you test whether y is 0, and if it isn't you test whether y is not equal to 0. The only thing this case do is cause edge cases. You should alway have an else branch, even if you don't expect that to ever occur.

y=[0 1];
if y==0
    disp('y is 0')
elseif y~=0
    disp('y is not 0')
else
    disp('y neither 0, nor not 0')
end

y neither 0, nor not 0

[Walter Roberson]

if y == 0
    fprintf('Your number is divisible by three, this many times: %d\n', divide);
else
    fprintf('Your number does not divide equally into 3, it can divide into three this many times: %d with remainder: %d\n', divide, remainder);
end

[Bozza]

Thank you all for the help so far. At the moment it sort of works, the problem is that it always states that the number is divisible by 3, even if it isn't. Is there something I can change the divide x/3 line to that finds the amount of times 3 equally divides into the number?

prompt = "Input a number:";
x = input(prompt);
%check x is whole positive number
y=mod(x,1);
if y == 0;
    disp('Your number is valid.');
elseif y ~= 0;
    disp('Your number is not valid');
    %I want to make it so that if this elseif is true, it asks the question
    %again
end
%test if x is divisible by 3
divide=x/3; %NEED TO CHANGE this to something that only finds the amount of times 3 equally divides into x.
%mod function to find the remainder
remainder = mod(x,3);
%output
if y == 0
    fprintf('Your number is divisible by three, this many times: %d\n', divide);
else
    fprintf('Your number does not divide equally into 3, it can divide into three this many times: %d with remainder: %d\n', divide, remainder);
end

[Walter Roberson]

if y == 0

Review your code to find out what you have assigned to y

[Bozza]

My code works now, only problem is that the divide output is not a whole number. I want it to output the quotient and remainder as whole numbers. Is there a function that can do this?

prompt = "Input a number:";
x = input(prompt);
%check x is whole positive number
y=mod(x,3);
%test if x is divisible by 3
divide=x/3; 
%mod function to find the remainder
remainder = mod(x,3);
%output
if y == 0
    fprintf('Your number is divisible by three, this many times: %d\n', divide);
else
    fprintf('Your number does not divide equally into 3, it can divide into three this many times: %d with remainder: %d\n', divide, remainder);
end

[Walter Roberson]

%check x is whole positive number
y=mod(x,3);

Does that line test if x is a whole positive number?

[Bozza]

It doesn't, but I'm not sure how to test if it is?

[Bjorn Gustavsson]

Check the help and documentation of the mod-function, look at the examples and test them to see how the function works and what it returns.

[Sam Chak]

Hi @Bozza

I think it is called modular arithmetic in mathematics. But I did not learn this in high school. I remember the Math Teacher discussed something similar on the topic of Prime Numbers. Didn't understand why it is not taught.

https://en.wikipedia.org/wiki/Modular_arithmetic

[Bozza]

I think I just fixed it with some simple maths. Leaving something for a bit can make you realise how easy the solution is :) Thanks for the help everyone.

[John D'Errico]

When you edit away all of your questions, you insult the people who spent the time answering those questions. You hurt answers, since then your question is completely useless for anyone else to ever learn from.

If you were going to delete the question, you should not be asking it in the first place.

Answer 1

[Bjorn Gustavsson]

Have a look at the help and documentation for while. Also from the question I guess that you're reasonably new to programming. If that's the case have a walk through the on-ramp material. That is designed to get you up to speed with programming, and supposedly no other way should be better than you browsing through that focusing on the parts that are of most interest and relevance to you.

HTH